Define "natural". There are plenties of species that practice rape.
I guess anything that happens in nature can be described as natural, but I think what some people here are suggesting is that rape is not a very successful strategy for succeeding in our natural world. It's not hard to find people who think that rape is the natural order of things - just visit any maximum security prison. But their view of rape is a minority point of view and most societies dispose of or segregate people who think like that either before or soon after they begin trying to spread their genes around. ;-)
"Define "natural". There are plenties of species that practice rape."
Name them, please. And be sure to name more than a couple, since you said "plenties[sic] of species."