I think a lot of it has to do with Groupthink and reinforcing each other's views. There are a lot of things (the genuinely appalling murder rate of transsexual prostitutes in Brazil, erroneously generalised as if they applied to the whole world, the faked up suicide stats which Mermaids promulgate) which if true would be absolutely scandalous. Because liberal feminists re-tweet these statistics and share them on social media without ever fact-checking them, the narrative that transwomen are the most oppressed group ever seems self-evidently true to them. Hence rad fems seem the most evil people ever to be (as it seems to them) cheerleading this insane level of violence. Except that of course that isn't the case. (The two women a week murdered by intimate partners versus one transwoman in the last ten years stat for the UK puts this into perspective - not to say that violence against trans people doesn't exist, or that it isn't horrifying, but it really isn't on the industrial scale it is against women).
The other thing which I think is there (because I was that lib fem back aged twenty-something) is a misunderstanding of the difference between a recognition of the role biological reality plays in one's oppression, versus a simplistic belief that this would somehow be to concede some sort of essentialist justification for one's oppression. It's taken me years to get my head round this (and I'm a bright, reasonably politically astute woman).
I think there's a danger that you (generic lib fem you - including my younger self) see the words "women are physically weaker than men..." and hear "women are the weaker sex..." and think mistakenly that rad fems are lining up with all those men they've had to fight their way past growing up, the men who said "women can't do maths, women can't throw properly, women can't, women can't, women can't..." When in fact the position is much more complex. It is that women are weaker on average, and uniquely vulnerable when pregnant and lactating, and that's just biology for you. But that none of this justifies treating women as less worthy members of the human race.
What biology does is (to use the whodunnit analogy I've used in the past) to provide oppressive men with "means, motive and opportunity" - the means is taking advantage of their greater physical strength, the motive is controlling women's reproductive labour and sexuality to ensure that it's their genes (the twatty men's) rather than any other men's genes getting passed on, and the opportunity is the patriarchal system they construct to provide a justifying ideology for that oppression. Biology facilitates those choices, but doesn't make them right or inevitable.
(Compare and contrast femicide and patricide, for example. Young men are physically stronger than older men - hence the massive social taboos against patricide! Taking advantage of one's physical strength isn't culturally inevitable or always culturally sanctioned. Where it's deemed to be a bad idea, all sorts of cultural ideologies grow up to keep unfettered male violence in check. Specially when the potential victims are male.)