He killed Wynne, then when Greagoir asked him what he thought they should do about the mages, Caerwyn said that equivalent response of "I don't care." Apparently that did the trick!

I've been playing through the game using the closest response to "I don't care" in most situations, and then angry/violent responses to racism and mostly negative responses when magic is involved. In-game Caer and VLS'v Caer aren't the same because the latter has Tesni to help him.