when somebody with an identity of some kind challenges your preconceptions, prejudices and stereotypes that doesn't mean you should question their identity.
what it means is that you should question your prejudices. 'cause that's what's got you confused, you see?
you humans...
it's actually a science v. philosophy argument. evidence v. reasoning. empiricism v. deduction.
the individual that challenges your prejudices is evidence that your prejudices are wrong; the idea that they are not as they identify because they don't fit your prejudices is medieval logic.