You know what I say? It's fanfic, let 'em both initiate it whenever the writer feels like! I mean, in canon terms any wincest story is automatically AU anyway, so who cares? Right?

Ha. There's me, sitting on the fence there! In all honesty, I can see both Dean and Sam being the initiators in different circumstances. Yeah, Sam is, or perceives himself to be, almost a normal person in abnormal circumstances, whereas Dean has completely embraced the fact that neither they nor their lives are normal, so yeah, Dean might be more open to the idea. And I think Dean needs Sam more than Sam needs Dean - that sounds silly, because if this show has shown anything it's that these boys are incapable of living with the other, but Sam can live that normal life, whereas Dean can't. Dean only ever had three things in his life - his dad, his brother and his car. Sam had a life, friends, an education - he may never go back to that, but he could.

But then I think Dean would perceive it as abuse or taking advantage of Sam - protecting Sam is hardwired into Dean's brain as 'Imperative A1' and I think he'd a difficult time getting around that. So I really don't know. I could one initiating as much as the other, so I don't see why people can't write both.