I could ask the same question about the man who claims to be Jesus.

You could ask it, but I think a correct answer would look quite different in the two cases.

I should preface this by saying that I am neither a psychiatrist nor a psychologist, and will welcome corrections from those who are. So, anyway, my understanding is that if someone thinks he's Jesus then either (1) he expects to have some super-Jesus-powers like performing miracles or offering teaching so supremely wise that following it will greatly improve anyone's life[1], and/or (2) his thinking in this area is so seriously disordered that it's a bit of a stretch to say that he actually "thinks" he's Jesus as opposed to merely saying it but not really understanding what that would mean.

[1] For the avoidance of doubt, I am not claiming that the actual Jesus (assuming there was one) had those superpowers; only that those superpowers are part of what is meant by "Jesus" in the context of someone claiming to be him. In case 1, his beliefs are falsifiable and will generally be falsified. In case 2, they are unfalsifiable but this isn't much of a steelman; the point is just that he's not thinking coherently.

What about the other case? Well, here my understanding is that (1) the people in question do not have falsifiable-and-will-be-falsified beliefs; they do not, e.g., think that their anatomy is different from what it actually is. And (2) their thinking in this area may differ from (e.g.) yours but it is not incoherent and they don't in any way resemble people undergoing schizophrenic episodes.

So, first of all: Do you disagree with me about this? If so, (a) on what points and (b) how do you suggest we go about determining which of us is nearer the truth?

Now, so far what I've said about transgender people has been purely negative -- I've said "no, they don't think X and don't have problem Y". Perhaps you disagree not about that but about what you (rightly or not, we'll see) expect me to say about what they do think. So let's proceed.

The model of gender they're working with goes something like this:

• Gender is not simply a matter of anatomy or genetics or biochemistry.
• What it actually is is a matter of social role-filling and self-perception.
• Therefore, someone who is seen by others and themself as female is female.
• This means that, e.g., there isn't a valid inference from "female" to "able to bear children" or "interested in having sex with men" or "not very strong" -- but there never was anyway; some people are infertile, some people have non-majority sexual preferences, some people are much stronger or weaker than average, etc.
  • It makes no difference to speak of to the perfectly valid statistical inference: if someone is female, they are much more likely to be able to bear children, much less likely to be able to lift very heavy weights, and so forth.

Do you think something in that is delusional, on a par with thinking you're both Jesus and John Lennon? It doesn't look that way to me. (As it happens, I think this is a better account of gender than any that makes gender a matter of anatomy or genetics or biochemistry, but at present I'm not concerned with defending that claim; the only relevant point is that it isn't crazy.)

In terms of this model, it's clear enough (I think) what someone means when despite having a Y chromosome they say "I am a woman". They mean: "I am much more comfortable thinking of myself as female than as male; I wish to occupy a female role in society, to use a traditionally female name, etc.". This would make little sense if "female" meant "possessed of a uterus" or "having two X chromosomes", but (see above) that isn't what it means in this context.

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Finally: Let us suppose that all of the above is, in some way I'm failing to see, totally wrongheaded, and that in fact there is a Right Way to determine someone's gender, and that Right Way is a matter of looking at their chromosomes or something, and that we therefore really are talking about "men claiming to be women". There remains what seems to me a pretty clear distinction between someone in that position and someone claiming to be Jesus-the-son-of-God. Namely: in almost all contexts treating someone as a woman despite their male-typical anatomy and chromosomes is easy and harmless, and empirically it makes these people much less likely to kill themselves. (And no one has yet found anything else that does.) Whereas treating someone as the Son of God probably means, e.g., worshipping them, which is a much less reasonable thing to ask others to do.

I repeat that my primary disagreement with you on this point is about whether transgender people are really much like people who think they are Jesus; the point of the previous paragraph is just that even if I'm completely wrong about that, it doesn't follow that we should adopt the position I think you are suggesting we should.