What do you think of people being able to change their genders whenever?

I've heard stories of men saying they were women to take advantage of women. (A rapist called himself a women so he could be put in an all womens prison.) On one hand you should be able to express yourself but then theres people like that who take advantage of it yk? I just think maybe there should be more steps rather than people just doing it but then again this makes things more dificult for people who actually feel they would fit better with another gender identity.

PS. Not transphobic/genderphobic or anything, ots just a concern