Yes, diplomacy is good, and it's not that Trump should never ever have agreed to meet Kim. Just not that early, not in that way, and not with these apparent delusions about how easily it can all be worked out. Among other reasons, because once Trump wakes up to the reality of how complex it all is and sees that his new buddy Kim really isn't going to give him anything important unless he gets major American concessions in return, I wouldn't be surprised if he goes right back to the 'fire and fury' stuff.
Diplomacy is done primarily by, you know, diplomats. Presidents get to swoop in and sign the deal in the end - but after a lot of preparatory work. Like the kind of preparatory work and long negotiations that went into preparing the consensus text of the G7 summit, before Trump decided to tear into that.
Now, of course, some preparatory work behind the scenes certainly did happen, and Pompeo went to North Korea - but when you look at the actual agreed text of the summit, you can't help but think that if this was all NK was going to commit to at this stage, then it was really too early to bring in the president, particularly in such a high-profile, one-on-one setting.
Before the meeting, the US was insisting on complete, verifiable, irreversible denuclearization - so full access at all times to all nuclear facilities, that kind of thing, like in the Iran deal. In the text of the summit, sure, North Korea does 'commit to working towards the complete denuclearization of the Korean peninsula' - but, as the text itself mentions, NK had already promised the same thing in its joint statement with South Korea at the end of April, in more detail. So the Singapore summit text doesn't have any progress on that point, nothing at all about the verifiable and irreversible aspects, nothing about control mechanisms or access for inspectors - and when reporters push Pompeo on that, he gets huffy about it and calls that question 'insulting and ridiculous and frankly ludicrous'. And says that he's very confident that Kim understands that there will be verification.
Well, you know, I and the world media weren't there... Trump and Pompeo were, and they may even be right in saying that Kim genuinely seemed inclined to accept more than the text states. But even if so, it's still a long way from 'he seemed to be okay with it' to actually seeing it happen. The negotiators of the Iran deal could tell them a thing or two about that.
I'm not sure he could have forced a concession this early in the game, no - but I am pretty sure he should've left the negotiation up to lower-level people with the occasional visit from Pompeo until he did get such a concession (with South Korea conducting its own negotiations at the same time in parallel). This summit and its timing seem to have been based on Trump's domestic political concerns, not on any sound negotiating strategy in the best interests of the United States.
It's possible. There is certainly a significant new factor other than Trump, which is the new South Korean president and his far more conciliatory approach to North Korea. I'm not sure yet if that makes the NK situation easier necessarily, but it makes it different anyway.
I think part of the problem is looking at it as 'the media'. It is indeed a pretty safe bet that just about anything Trump does will be criticised by someone in 'the media'. But the media isn't monolithic, and at least the quality papers do have standards that keep them to some sort of editorial line and some level of consistency in what they approve of and what not. As do liberal columnists or op-ed writers. I don't believe most of them reflexively oppose whatever Trump does as you suggest, each time flip-flopping at the same time as Trump except in the opposite direction. Though no doubt it is true that you hear them the loudest when Trump is doing things they oppose, and the praise when he does stuff they agree with will be a lot more muted.