Testosterone is correlated with sexual aggression. Chemical castration is a treatment for rapists after all.
Just personalize the idea, your sister or female significant other was thrown in jail, and then housed with a male who is a trans woman who has sex with her with or without her consent and creates an ongoing consequence that is impossible if trans women were not there
That would be the expectation you would start with to form a conclusion
Sex in male prisons does not result in pregnancy
Sexual assault does not hit some magic breaking point where it becomes an unacceptable risk at the chance of impregnation. If there is a significant risk of sexual assault, then the prison has fundamentally failed and that is the thing that needs fixing.
It simply doesn't matter if someone is trans or not, cis people are just as capable of sexual assault, and prisons must be protecting all inmates, not only cis-women, from assault.
its not nearly as gendered as you are making it out to be, this a condition statement satisfied by some gendered combinations
Why would a rapist stop wanting to rape regardless of the state of their genitals? Is sexual violation with a penis so much more horrific than other violations it deserves special consideration?