Rape is a very big sin, probably next after murder.
According to rosicrucians, if you have an orgasm while being inside eachother, you switch pieces of Karma, putting one piece of the other very deep into your own being. All religions know about the purity of virgins, virgins being sacrificed etc. Having sex with a lot of people therefore screws up your Karma, because you will have to deal with it, which even a monk may take a lifetime.
Forcing a girl to take your crap Karma and thus ruining her entire being should be punished by death.