As far as I am concerned, the main part is that you can't do any major structural changes on the base level. XX will remain XX, XY will remain XY, no matter what the outside looks like. A trans "man" is a female playing, to some extent, the role of a man in society, and they can never take that role fully due to their basic construction. A trans "woman" is a male doing the same, with the same caveat. At best any trans person is somebody in an in-between situation, not able to become the opposite sex they claim they want to be, but unwilling to embrace what they are, and so stuck to being an actor trying to play the role of what they'd like to be.

Now I do think people should have the freedom of choice to do that, with the caveat that they should not try to push themselves into what they are not fit to do, like males competing in sports reserved for females because they have an unfair advantage there due to their genetics, or trying to lie about their actual sex when looking for partners for sex or especially marriage.

So I'm okay with trans people in general, and willing to play along with their roleplaying, but if, and only IF they are willing to admit that it is roleplay, not a real change. A transwoman is a transwoman, something that will remain always as a separate category from biological women, same with transmen. So it is a mental disorder, but there are plenty of those that can still allow the person having them to fit into society without causing any major problems for themselves or anybody else, as long as they want to do that, and are willing to fit in.

That tolerance stops however when they start to demand that we'd pretend they are no different from the real men and women.

And I'd reserve a special category of hell for those troublemakers - seems to be mostly men - who don't even bother to try to disguise themselves well enough that you might actually mistake them for the opposite sex, like men who just put on a bad wig and lipstick and then look for situations where they can raise hell because somebody "misgendered" them. For heaven's sake, at least TRY a bit more if you want to do that roleplay.