The issue comes back to Reasonable Doubt ultimately anyway. That's why from a pragmatic perspective the alternate burdens of proof play a lesser known role when people discuss self-defense, etc. There's intentionally no probability attached to these things, except preponderance of evidence which one could say 50%+, at least for only two realistic scenarios. But the 'better 10 guilty... 1 innocent' does attach a vague ballpark to reasonable doubt, 90%+, and that sort of damages 50%+ for two opposing scenarios because in effect you don't need 50%+ that it was self-defense, you need 10%+ of self-defense to establish its no longer 90%+ to be guilty.
And that's what it comes down to, we've decided that people don't go to prison or the chair unless it is 90%+ and that's all the defense needs. You may feel self-defense should require a lower bar, a partial shifting of the burden, but its the degree to which someone needs to prove that which really matters. No state has self-defense dialed up so high zero justification beyond the claim is needed, nor any so low that proof by the defendant needs to be beyond a reasonable doubt. What you're essentially arguing is that you object to the 'better 10 men' aspect of things. Nothing wrong there, it is a statement much easier to say as a theoretical then swallow in application since it means swallowing someone you think is 89% likely to be guilty being back out on the streets. And when you throw in recidivism rates, one would have to contemplate that if 1 in 2 murderers will do it again then for every one innocent man in prison for murder we essentially killed 5 people from not putting those 10 behind bars.
There's no getting around it though, if you feel 'more likely than not' is the proper standard for a self-defense case, you're saying its okay to sentence someone for murder if there's a 49% chance they had self-defense. So again, while self-defense does require an affirmative defense much of the time, the level is essentially whatever is needed to make it reasonable doubt.
I understand the entirety of a jury trial rests on the concept of reasonable doubt. And I do believe that having to prove the guilt of the accused is the state's duty. However, I also believe that if lethal force for self-defense is claimed, it should be on the defendant to justify their claim. I will stand by that rationale, even moreso in light of the Zimmerman trial, because I think the taking of another life is something that should require more thought and effort than simply making a statement to police and refusing to testify at trial. If you or I kill someone fearing for our lives, it should be on us to prove that the situation warranted such a deep fear that deadly force was necessary. I do not think that "I was losing a fight I started" is a good enough reason to use deadly force, except -- as pointed out previously -- in the rare event that the fight flipped sides to the point that there was (a) some effort to try to remove oneself from the conflict and (b) the other person refuses to allow a retreat.
Now in terms of intentionally murdering someone with self-defense in mind, that's much harder than it sounds like. There's no dispute who did the killing, and a SD claim has to be made pretty early on. So the investigators don't need to jump any hurdles to investigate the accused nor split focus to other scenarios. They will be digging around for everything, internet records of you googling self-defense laws in recent months for instance. Emails or witnesses establishing you knew the man, etc, and had a hostile relationship. They're probably going to find something unless you didn't know the guy or were very careful. In either case it is a hell of a lot easier to kill them and not stick around to claim SD. We don't get a lot of bogus SD claims attached to prolonged preparations for the simple reason that anyone that cautious and dedicated is likely to try a safer route. Upping the burden on the defendant to prove it was self-defense is really very unlikely to cut down on murders.
I would argue that, if the investigators perform a thorough investigation into the claims and fully collect all forensic data and statements at the time of the commission of the crime, a self-defense claim should be fairly easy to justify. I know you do not want to revisit the Zimmerman case, but I will use it as an example of how not to investigate a crime, because the police never checked Martin's phone record to see if he was on his mobile at the time of the altercation. It took the person Martin was speaking to to come forward before anyone realized there was another witness to the crime. If the police investigators cannot do their job in a thorough manner, then they are basically conceding that there is little they can do to determine the guilt or innocence of the accused and are simply taking him/her at their word that their version is not only accurate but truthful enough to warrant no further action.
The police are only human, but in the investigation phase, if there is any hint of a possible crime committed there should be a thorough investigation completed to determine if charges should be filed. Most seem to agree it was not done in this specific case, and in many other cases there are plenty of defendants who are either wrongly accused or wrongly convicted because of a botched or corrupt investigation. I don't think the human element can ever be removed, but I also don't think a crime as severe as a potential murder should be swept under the rug simply because the defendant gave a statement that claims lethal self-defense was necessary.
You should try it some time, I've had to help draft a lot of ordinance and such over the recent years, especially of late, and its changed my perspective a lot. It hammers home that law often requires specificity and that criticism of law is best done the same.
I once took a summer workshop when I was in high school which put us in the positions of pretending to be state legislators. I'd much rather watch paint dry, thanks. 
I do know how the creation of laws works and the issue of unintended consequences. However, the claim I was trying to make still stands: when a verdict is perceived to be unjustly reached through a fair process, the laws which created the outcome should be revisited and rewritten so that a person who commits a crime can be properly brought to justice rather than simply acquitted because the law as written does not fit the crime they are accused of. I strongly believe that we should not be putting innocents in prison, but at the same time I also strongly believe that when the evidence points to a criminal conviction, that conviction should be able to be reached without confusion by the jury.
I agree with you on the greater point that writing laws specifically to address one instance of a criminal case is terrible policy. It results in policies like having to take shoes off at the airport because one person tried to smuggle explosives in their shoe, but yet -- thankfully -- underwear is still ok to have under one's clothes rather than stripping naked to board an airplane after someone tried to smuggle explosives in their underwear. Still, the trial is useful to illustrate the point of why I think the law should be altered but I will do my best to try to speak in general terms.
I will try to make this the last reference to the case in our legal discussion, because I really want to make this point:
From the beginning I have objected to the interpretation of self-defense as offered by the jury in the Zimmerman case because the jury seems to have never considered that both men had a right to self-defense. The fact that I did not initially research the letter of the law is beside the point, because my main concern is that the law was never applied fairly. I realize that Trayvon Martin was not on trial and can never be on trial since he is dead, but this specific case had "manslaughter" written all over it from the beginning. But now that the jury has spoken, I am trying to come to terms with the fact that a series of botched legal processes has resulted in a guilty (as I see it) man walking free. This is the way the jury process works, but it does not make it any easier to reconcile with how I perceive justice to be served.
Part of my interest in the trial was my fervent hope that a young black man could be seen as a person with every right to be walking home from the store without being thought of as a thug or criminal, with his own right to defend himself against an aggressor who has actively pursued him for no good reason. What I got instead was a sloppy police investigation and a prosecution which failed to bring the salient points of the conflict and instead relied upon the how instead of the why. Nothing in the written law can change a terrible prosecuting attorney from failing at trial, but I think as a non-lawyer I probably could have come up with a better series of witnesses and arguments to get a conviction than the prosecution did.
It comes out today that the jury instructions of the state of Florida has a line which reads "an aggressor cannot claim self-defense and that a person who aggressively follows another person is an aggressor." The defense successfully argued that this language should not be included with the jury instructions, and the judge allowed their argument to stand. That one line is the entirety of the prosecution's argument against Zimmerman -- that he actively pursued Martin and caused his death. That was the whole reason for the outrage against the verdict, because it was obvious to everyone involved that Zimmerman made choices which resulted in him being the aggressor. An aggressor, by law, cannot claim self-defense. This is why I argue that the definition of "aggressor" needs to be made more clear, but I do not have the time or inclination to rewrite Florida's laws for them, so I suppose the entire exercise is moot...
Everybody lies, and people often say untrue things they believe are true even when they clearly contradict other things they're claiming. Perjury is - with good reason - tricky to prove. Eye witnesses to events, especially ones involved in them, routinely not only remember things inaccurately but remember things they want to be true, and the more they replay it the less accurate that memory becomes. This is very true of traumatic events and especially of ones where your own actions are under judgment. I've known people who shot enemies in blatant justified circumstances but before long were sick with grief and uncertainty over it and rapidly had their own version of events mutate from what others witnessed to be more guilty. I've known others who totally fucked up in a battle and before long had rewritten events to include things that justified it that didn't happen but which they truly believed did and hell I've seen others involved rewrite their own memories to be truly convinced it did. People make lousy witnesses, especially for almost any occasion we need good ones.
On any criminal matter he said she said generally results in a not guilty if that's all there is. It doesn't matter what the crime was, shoplifting or rape or murder. Now you keep talking about justification but you seem to keep ignoring that the need to justify a killing is not under discussion, its already there quite firmly. Once it has been established you've killed someone you must explain why, if you can. Inability to do so, at all or insufficiently doesn't conclude the matter though. This is why I've advised you to keep to hypotheticals.
Example: Two men are found, one dead, the other unconscious clutching a gun. He reports to have no memory of the event, but all evidence conclusively demonstrates he shot the other man.
Now this man can't really claim self-defense and justify it because he remembers nothing, but the case is not over, the state must still prove beyond a reasonable doubt that it was a murder. Again, this is the hazy nature of affirmative defense, it implies a burden of proof but it still ultimately comes back to the beyond a reasonable doubt burden on the prosecution. Yet the defense can offer nothing, the defendant remembers nothing, the defendant does not recognize the man. Now based on your prior remarks you think this person is well setup to escape justice, but not so. Motive, means, and opportunity. The last two are established, the prosecutor needs to come up with the first, if he can show the defendant did know the man, well that's pretty solid - though not definite - proof he's lying but that lie does not necessarily mean he's a murderer. He may well have met the man in passing, in his memory, but blanked out the altercation they had at the bar that led to the fight and killing, and been afraid to admit he knew him at all, or later remembered him but been afraid to change his story. From what you've been saying in this and recent posts, that act of not apparently not telling the truth should result in a conviction. But this is where we get into the practical, because that bar altercation is going to have been witnessed, forensic evidence may exist indicating who started the tussle, and so on, and it has to convince a jury beyond a reasonable doubt. Its not that rare or impossible, most murders that make it to and through a grand jury do result in convictions.
I know everyone lies to one degree or another. I also know that when someone is a habitual liar, and provably so, their word should not count for much at their trial if their lying habit is exposed publicly. Once a jury believes their credibility, there is not much that can be done about the outcome, and that is where the conclusion of this particular trial has left us.
Look, we can argue hypothetical situations until the cows come home. It does not change the fact that the application of the law in Florida leaves much to be desired. If it is possible for someone to initiate contact and start a chain of events which results in the other person's death and they are not an aggressor, then we need to question what it means to act aggressively. If I shout insults at you until you get angry enough to strike back and I shoot you dead, I am apparently justified in claiming self-defense, even if you only get close enough to give me a bruise. Probably not even then, as long as you "look menacing" such that I can convince a jury that you are a fearful character. Am I being aggressive by provoking you to action? If I follow you and, without identifying myself or my intentions, try to chase you down simply for walking home from the store, am I acting aggressively? If the two men in your scenario were involved in an altercation that many witnesses can prove was a mutual escalation then a self-defense claim is more probable as "heat of passion" is an excuse for an accidental killing. If one definitively provokes the other, the one provoking the fight should not get to claim self-defense without a pretty high justification for acting with deadly force.
