It is a mental illness in almost every case. Barring the outlier cases with chromosomal or physical developmental abnormalities, if you have a penis and think you are a woman, you are objectively incorrect.I understand I'm not going to agree on this topic with most people. But any time we're classifying a whole group of people with a large brush, we should take a step back and really give some critical thought regarding this characterization -- whether that's due to their LBGTQ status, race, or some other particular reason they're being grouped that way.
There are nutjobs from all categories of people. No one here is wrong for not wanting to be around loud, obnoxious assholes. But let's not over generalize either.
I view it the same as I would schizophrenia. They are convinced "the voices" are real, but they aren't. I don't go around telling them that, "oh yeah, the voices are real, I hear them too"! I'd tell them they should get help, something is wrong. If you support beliefs that are provably incorrect, you aren't helping them, you're harming them by enabling.