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 you 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 selfish and lust-driven AT BEST. The other reasons, are just varying degrees of sinister. There is not a noble reason.
You could kill someone for a noble reason, however.