Heterosexual refers to their sexual orientation, not their wish to label themselves as women, so in respect to danger to women, transwomen with fully functioning male bodies who are oriented to desire female sexual partners do not differ from the men they used to be before they declared that they were transitioning.
Syracute says "It is heterosexual males that create the most danger for women." - Yes, and that is why transgender but heterosexual males have no right to be in places where women are undressed in a hospital ward, under stress because of previous abuse by men, or vulnerable and imprisoned where they cannot get away from men. Also there is the psychological effect of their presence as well as the physical.
Do any advocates of their presence have any suggestions for how to screen ANYONE, not just transgender people, to ascertain whether they could become a threat to women, without being invasive or humiliating to anyone? That would be extremely useful, and would prevent a lot of rapes, injuries, and abusives.
As a bonus it would also save a great deal of time and money for the agencies which have to deal with the after-effects - the medical and counselling sessions for the victims, and the investigations, arrests, trials and imprisonments for the perpetrators.