I totally agree with Hully here:
I think, in simple terms, there are raving extremist loons in all walks of life and the raving loony extremism comes out in whatever their "thing" is, be it religion, transactivism, racism etc etc.
And no, condoning or threatening violence is never acceptable. I'm sure that violent transwomen and queers exist, and they're wrong. That said, Brennan's statements are themselves extremely violent-sounding and inflammatory. She also consistently uses language that implies she is referring to ALL transwomen or ALL 'queers' rather than a small, loony minority within those groups.
LRD mentioned starting a women's political party. Much as I like the idea, I wouldn't be able to support any political party that propagated hate speech about minority groups in this way.
'Queer' can also mean lots of different things according to the context. In some circles it's simply used as a synonym of gay or lesbian.
There's a real contradiction between Brennan saying that she rejects any identity imposed on her by society, and then attacking 'queers', because the term queer (in the 'queer theory' sense) was coined as one possible way for people to describe themselves when they want to embrace an identity NOT imposed on them by society. So in theory it seems to me that rad fems like Brennan and self-described queers should have a lot in common - they are both objecting to roles assigned to them by patriarchal/heteronormative society. But obviously not!
Brennan is very keen on putting people into the right pigeonholes, it seems to me. If you fit her definition of a woman, then you are free to assert your own identity in your own way, but if you are too trans or queer or whatever, you're excluded and given a pejorative label. She's entitled to her own views, of course, but as I say, I prefer a more inclusive brand of feminism.