Killing is actually worse, I'd say.

But the reason you'll get so much pushback for saying so is because of this -- and this is the real ass answer:

When you kill somebody, that's it. They're gone. The last thing they did before killed them, is the last thing they did.
But the sheer ongoingness of what a rape does, to a person is completely incalculable. It cuts through everything they do from then on. And the reason the rapist did the rape, was for selfish lusty reason AT BEST. The other reasons, are sinister as shit. There is not a noble reason.
You could kill someone for a noble reason however.