No has a brain transplant. No one has had a brain transplant or will have a brain transplant.
It is a weak attempt to leverage in ‘wrong body’ and has nothing to do with not disclosing the sex your (general you) body is before having sex with someone.
Whoever initially devised the brain transplant exercise for this purpose obviously thinks this is a clever exercise, but it is not. This is just another failed analogy. Just like being born in Dudley and moving to Berwick. Just like being female is supposedly “ a constellation of statistically linked attributes - including genotype - that together match a pattern we identify as sex.” These don’t work because they are fatally flawed from the outset.
No one has had a brain transplant.
And what is the only true statement is that any male person can only ever be a male person. They are male in every cell of their body. If they claim to live like are a female person, they are only ever living as their personal conceptualisation of how they believe a female person should or would live.
They live their life navigating the world with a male body and dealing with that body and how society deals with that body. If they make extreme body modifications it is still a male body, just with extreme body modifications. Not a female body. They don’t navigate the world with a female body, only with a male body with extreme body modifications.
A cavity that has been created in a male pubic region is not a vagina. It doesn’t have any role except to insert objects into. It doesn’t even act ‘just like a vagina’. It never has and it never will. It is not a vagina despite some people claiming that it is.
Someone making extreme body modifications to their body does not give that person any right to not disclose their sex to a potential sex partner. A decision which will negate the consent of that partner and mean the sex is not consensual. Because every person has a valid and reasonable expectation to know the sex of the person they are about to have sex with.
No brain transplants. There are No wrong bodies. A modified body is always a modified body. A male person has always interpreted life as a person with a male body their entire life. Even after extreme body modifications.
The logic can never be anything else.