I think this kind of adventure is extremely group dependant. I had Sigwin very strongly imply that the curse was not *his* doing, but rather a result of the bargain not being fulfilled. He was lying, of course, but the players didn't know that and it made the players pick a side. "You think that such a bargain can merely be cancelled with no repurcussions? We elves are *magic* beings, our promises hold *magic* weight! The only ways out of this are to give me the baby, or kill me. And if you're considering the second... good luck."
Of course, this adventure might just not be for your group. Some players don't do well with ambiguous moral quandaries.