"Again, I'm not claiming that they are a woman.
I repeat: they aren't a woman!"
Let's leave out the next bit where you contradict yourself and, "for the sake of argument", you imagine a "mysterious sense" in which men "really are" women.
Let's go straight to:
"they want to be accepted by a male partner as being a woman, and changing your physical appearance makes that easier."
Now let's leave out this bit: "So whether they are a woman, or just have a belief that they are a woman" and go straight to:
"So . . . why not get surgery?"
What we have left, if we cut out the bits where you contradict your opening statements is:
"Again, I'm not claiming that they are a woman.
I repeat: they aren't a woman!
They want to be accepted by a male partner as being a woman, and changing your physical appearance makes that easier.
So why not get surgery?"
Now, let's get some clarification of who you are talking about: who are "they"?
(Don't double back on yourself and answer "men who think they are women" because you don't need to conjure up that imaginary scenario "for the sake of argument".)
When you have clarified who "they" are . . .
Why do "they" "want to be accepted by a male partner as being a woman"?
(No, not because they are "men who think they are women" - think of another reason or reasons why some men "want to be accepted by a male partner as being a woman".)
Go on, you can do it. It will help you to avoid these mental contortions where you say you don't believe something but then, ironically, keep constructing imaginary worlds where the thing you don't believe is true. Try imagining a world that is congruent with your opening statements:
"Again, I'm not claiming that they are a woman.
I repeat: they aren't a woman!"