It is clear that the mental health profession finds that they are not harming themselves or anyone else, or they would be treating them differently. You are free to disagree, but they're the experts.

People choose to have surgeries that are not medically necessary for myriad reasons. And they're allowed that choice. So that's not a valid argument (that the surgery could cause them physical harm or be seen as physical harm).

It's trickier to say definitively whether they are or are not harming anyone else. It's clear they are not physically harming anyone else. That's probably sufficient. Emotional harm is awfully tough to prove and never black-and-white...Imagine a mildly or severely depressed parent of a young child. It would be much easier for a concerned 3rd party to prove that the parent's depression was physically harming the child (say the parent never feeds the child) than emotionally harming the child (through neglect, say...mommy never gets out of bed). In the case of physical harm, one would expect authorities to remove the child from the home and place him/her with somebody who will feed them (to protect him/her from harm) and require treatment of the depression as a condition for return. That's different from treating a person for depression against their will. In the case of the possible emotional harm (if proved), you also have to weigh whether the child would be better off (less emotionally harmed) if removed from the home, which won't always be true.

Your statement that you see "their requirement that society treat them as socially similar to the body that they now present as inauthentic" puzzles me. Can you clarify what you mean by that? You (or anyone else) seeing them as inauthentic should (and does) have absolutely no bearing on what is best for them and what the mental health profession has decided is best for them.

Prosthetic limbs are inauthentic. Is somebody wearing a prosthetic leg requiring you see them as a 2-legged person inauthentic?

You have said that a few times in this thread, but it's not true, you know It is demonstrably not true that this is the only "mental health issue" where treatment includes taking their viewpoint as valid. One other example I can think of is dementia/Alzheimer's Disease. We don't keep insisting to grandma that she better remember she's married and has grown children because that is THE TRUTH. Forcing the truth is seen as unnecessarily upsetting and worsening her condition, so everyone goes along based on the recommendation from the doctor that this is what's best for her. Some delusions and paranoia can also be treated this way. There are certainly others.

The fact that gender dysphoria is recognized as a diagnosable mental illness shows you that the profession knows that the person's perception is not "valid." By your own admission, the profession sees depressed thinking, obsessions, compulsions, etc. as disordered and to be treated. One of the ways available to them to treat this disordered thinking is to physically alter the brain chemistry through psychotropic medication. Physically altering the body of gender dysphoria patients accomplishes the same thing--removes the physical source of the disorder.