It is the logical conclusion of where self-ID of sex takes us.
Those men on long sentences may well see the advantage of claiming to be female, despite never having had any history of transgender on the outside. Huntley never claimed to be transgender before his incarceration. Men on shorter sentences may be less likely to claim to be transgender since they'll be released before they can get a transgender board assessment in prison.
Those on long sentences are very likely to have been convicted of violence and sexual offences against women and children.
So those men who self-defining as women will be the absolute worst of the men in men's prisons. And those who pose the most danger to women.