Barring mass surveillance, we are not ever ever ever ever going to be able to prove that most rapes happened beyond a reasonable doubt.
Normal rapes are “I said ‘no’, but I was too drunk to fight zir off”; it’s “I said ‘no’, but then I froze up and didn’t resist”; it’s “my partner was abusing me and I knew that if I kept refusing he would hurt me”; it’s “I couldn’t hit a girl”; it’s “he pinned me and I couldn’t move”; it’s “I fought back but it didn’t leave any marks”. Rapes that are provable are rare, they are the exception, and smart rapists can easily avoid them.
If we don’t allow colleges to expel people for committing rape, or we use a relatively high standard of evidence, then the victim will have to see his rapist across the quad, in the cafeteria, in science class, at parties. And the rapist has access to a new crop of vulnerable people, and she can rape again and again.
If we do use a relatively low standard of evidence, then abusers can easily get their partners expelled from school as a punishment for leaving them or as a tool for isolating them from their social group. Abusers already make their partners think the partners are the real abusive ones; do you think they’ll have very many problems stepping it up to “…and if you leave I’ll report you to the Dean”?
So it goes.