Admittedly, telling the villain that something is "the right thing to do" is pretty much a guarantee that they won't do it. Not that that should stop the hero from trying.
Actually, you could try a kind of reverse briar patching, and say that something heinously evil that the villain would actually want to do is "the right thing to do", so they don't do it, just because they think you want them to.
Try it in your next game and let us know how it works out. (Preferably with a GM who doesn't read this comic...)
Jabba: Enough talk! Time to throw them in!
Boba Fett: Shouldn't they be frozen again first??
Han: Yeah, yeah! You need to delay this execution thing!
Luke: Let us go, Jabba. It's the right thing to do.
Jabba: I'm not getting cold feet. I don't even have feet.
Jabba: Wookiee-gram! Provide mirth!
Chewbacca: Um. Telegram for you: I'm dressed as a Wookiee. Stop.
Chewbacca: I'm trapped in a bad joke and I can't. Stop.