Much simpler answer is this: Don't accept the premise of assholes. They are not asking out of a desire to discover truth, but out of a desire to frame any discussion in terms favourable to their position: that there is a distinction between body and mind and that "female brain in a male body" is a valid premise on which to found an argument.
As much as I like the various answers being given and have given my own at times this is actually correct because they're just pulling a bad rhetorical move they hope you aren't noticing. You can actually "expose" it by accepting all their premises in the three examples. At no point can we get from their premises being hypothetically possible to the "truth" that trans beliefs are actually true in reality. They'd still have to show they've changed the biological sex of their cells and they can't do this. They
have to attack the connection between gender and sex because it's the only way to divorce things from the material reality of now. That's their goal, but there's no intermediate step to get there from an irrelevant hypothetical.
Additionally, that thing makes another common troon error:
Except you
can't. This also skips a step of logic by asserting that if you experience something you can change that experience as a premise. But one can easily realize this doesn't apply to
everything. The race discussion above actually illustrates this because most of them would argue the problem with transracialism is that you can't experience being another race. They're trying to argue that by changing their appearance they can change what gender they're experiencing but this assumes you can both know and control what gender other people are treating you as. The real problem isn't that you can't control this, it's that you can't
know this. Just like with race you have no frame of reference for experiencing how any other gender is treated so can tell that you're being treated as it. Your "gender" is held entirely in the mind of the other person. For all you know they could be treating you as a potted plant or as the color blue. You can't
truly know anything they're experiencing or thinking or whatever, that's what makes them an entirely different being from you. This is a something they pretty much just dismiss, everyone thinks like them all the time which is why they're so quick to project or explain what someone else "really" thinks.
If you peel away the gender/sex nonsense you can see that their real belief is that they believe that simply changing something cosmetic about themselves will fundamentally alter how everyone will treat them
as a person. This is a fairly common low level belief, maybe you exercise and lose weight so people won't call you a fat slob anymore, but they make it the essentially the only thing. Then they reify it under a belief that this will change material reality somehow*. The gender thing is essentially just their own hangups about gender that they then project onto "society" since society itself is nothing but outputs from their inputs. The reason so many troons don't change anything about the personality or hygiene habits or anything else is because they fundamentally feel the problem is everyone else, if they could just be manipulated into seeing them "correctly" everything would change. Their body being wrong is just easier to accept than that their personality is responsible because it means they aren't doing anything wrong, it's just circumstances beyond their control. (Hence the need to assert that gender must be something under their personal control.)
*I would argue this is because it means nothing is truly ever outside their control, they just need to figure out how to manipulate it.
