I am pretty sure if an 14 year old girl is pregnant, people are about as opposed to it as they should be to a cosmetic double mastectomy at that age. (That some people are totally fine with a child getting her breasts amputated is horrible.)

You gotta meet some criteria to have people be happy for you if you're pregnant. Being an adult, for starters. That same criterion that trans people don't want to apply to their transitions.

Pregnancy potentially ruins the body and sex life of one person, and creates another, perfectly healthy person. Which is why people are happy.

Transitioning certainly ruins the body and sex life of one person, and does not create anything good.

It is very simple, really. The difference is the baby. Giving birth can totally mess up your body, but there is a baby that makes it worth it all.

Cutting off a man's genitals does not produce a baby. Well, not outside Greek mythology, in any case.