Rape is bad because that is how Freddy Krueger was conceived. So probably best to not have more child murdering creeps in the world. Why the Islamists love doing it so much.
Because sometimes buttcheeks touch together in the process and that's not sanitary. Babies are supposed to come out of there. It's on Wikipedia, OP, do your research.
Rape is only bad when it’s done outside of the context of total war. It can be a way to break bucks and to ensure the genetic legacy of the conquerors over the conquered. Thus this ensures the strongest genes are spread. World peace is a mistake for the longevity and genetic health of the human race.