Our prison system is utterly fucked. It fails women horribly who are, for the most part, imprisoned for non-violent crime.
The feminist analysis covers the different reasons women are jailed, the disproportionate impact on families when mothers are in prison, the almost ubiquitous background of domestic/sexual/childhood abuse imprisoned women have and more. Allowing natal males to enter the female estate only further marginalises this very vulnerable cohort of women.
More widely, we can look at our prison and penal system as a whole to explore the widespread institutional failings that also affect men (and trans people). While feminists can and should focus on women and unique issues like pregnancy while incarcerated, it's likely that their work on prison reform would, if successful, benefit male prisoners as well. Better mental health care, better educational opportunities, better facilities, fewer short sentences, better reintegration services etc. would benefit everyone.
Radical feminists like Julie Bindel have been doing such work for decades. Funny that TRAs like Ash Sarkar enjoy denigrating them while doing fuck all themselves.