Actually, I think they should both take responsibility for their own behavior. I don’t know when that started to be frowned upon in so-called conservative circles.
Children are not punishment. They are to be loved and taken care of. Hating your former spouse (or one-night-stand) is no reason to disown your own children.
Regardless of whether or not the tables were turned, both people involved in the conception would still be held responsible for raising the baby. Had it been reversed, the girl would have gotten custody of the baby and would still have been responsible for raising the child. Just because the boy is the victim in this case doesn’t mean he can dodge his responsibilities any more than the girl would have been able to had she been the victim.
The big difference if the tables had been turned would be that the girl would have had the option of choosing an abortion, the boy had no such option available to him.