Why should I write fic that's horribly cruel to Sam as penance for cruelty to Sam? That makes no sense!

Plus, if I wrote incest fic, it would end up horribly bleak and scarring and be intensely cruel to Sam, and you don't want that.

I think you should do it. And then write a Sam/Riona sequel which is all ice cream and puppy dogs (but no ice cream/puppy dogs; ever since I saw people slash letters of the alphabet, I've become convinced that everything has slashfic).