Sure you don't see a problem. However, they are parents and parents think about things in an entirely seperate fashion. He's not in a position to raise a family if an accident were to occur. He would have to limit his potential and perhaps lower his lifetime earnings by a signifigant percentage. That, in itself, would make the rest of his life harder .

Also there's the whole social aspect. Although it's not as much of a taboo thing now, when they were growing up it probably meant you were a slut if you were pregnant at a young age. If they're a religious group they don't want their son's sins coming out to haunt them.