It's a direct consequence of a theory that says bio sex is irrelevant and that gender is our primary characteristic. Defend the theory, you can hardly disallow the logical end points.
I don't ascribe to any theory that says that. Bio sex has hardly been irrelevant in the lives of the trans people I know. There is a conflict for them between bio sex and gender. That is far from the conclusion you're making. And no, even then, telling lesbians to "suck d*ck" is not a logical end point, any more than "all men are dogs" is the logical endpoint of feminism.