health is correctly derived as being instrumental to the terminal value life, the same does not apply in the case of homosexuality

What is "health"? I mean the most obvious definition about happiness or ordinary functioning or whatever would make this a bit tautological. And surely a lack of health doesn't only apply to things that would kill you, and you're presumably happy with medical practice usually taking this stance. The importance (and definition!) of health goes beyond the extent that it's a prerequisite for life.

If we lived in a society where we all needed to reach high things every day, then short people would be disabled. I don't think physical health is as objective as you're making it out to be. It depends on what physical skills are needed and expected by the surrounding environment.

that is, if they do not essentially turn out to be value judgements, then I agree that classifying something as a disorder is an empiric statement, because then the definition of disorder would be empiric.

The basic definition of a mental disorder is rooted in whether or not it causes some inability or difficulty to function in society. It's a value judgement by the society, in that it depends on what skills society requires of you, but not a separate judgement by the individual evaluator. Someone from an alien society should be able to study how ours works and pick out which mental behaviours create social integration problems. Yes, implicit in saying that homosexuality isn't a mental disorder is the fact that the desire for a nuclear family is not a skill that our society requires of everyone. But this is a true statement about how our society works, and has been for a fairly long time.

The statement that homosexuality is not a mental disorder is saying that it does not cause inherent distress or pose a barrier to functioning in ordinary society. It was put on the list of disorders because it was believed to be comorbid with (and possibly causally associated to) many other psychological problems, and taken off when this was found to be untrue. No more, no less.

I am not sure how it could even be evidenced in the first place, when you take conservation of expected evidence into account.

There is no reason to reference that. Look, it's really obvious from your comments that you just read the LessWrong sequences and now think you're better off by throwing Bayes' name into everything and using the word "empiric" a lot. Your arguments didn't get any better; you just found fancier words to dress around the same ideas you started with. The community there likes to dream up these huge ideas of "magic rationality skills" letting you sweep over any discipline you want with basic critical thinking skills, but it doesn't actually work. Yudowsky isn't the first one to think about how evidence and knowledge work, and the people in these other fields are not making the kinds of silly basic mistakes he likes to attribute to them.