No one wants vulnerable men to be beaten up or raped in a male prison.
The problem is, deciding that men who identify as women shouldn't be in the men's, so therefore they go in the women's. That's not the solution.
You can't just use the women's prison as a dumping ground for vulnerable men. What about old men, effeminate men, gay men, disabled men?
Women aren't weak men. And subjecting them to the presence of males, however much you personally may deem them not a risk, is wrong. Women prisoners are not there to validate male prisoners!
Most women in prison have significant issues. And the presence of men would exacerbate those.
One of the major issues over this, for me, is the expectation that women just soak up these problems. Because they're not considered, in any way.
What they want, need, require is immaterial to the validation of men.
And this is why feminism is so necessary. Feminism advocates for women.