> Women prisoners have been sexually assaulted, raped and impregnated by males who were transferred in to the female prison estate

Those occurrences are terrible, no doubt about it.

When designing policy, we need to look at both directions: How many trans people get raped because they don't get transferred? So far all the data I have seen indicates that trans people are far more likely to be assaulted than to assault.

It seems to me that we should choose the option that results in the fewest assaults.