You know, there are shows where I really don't see the slash/incest. For example, I can't see any ship between Nathan and Peter. I just don't see it. With SPN, it's the setting that makes it believable for me - I mean, the Winchesters basically lived in a closed society of three where Sam and Dean where the only ones even close in age. And the fact that John kept hammering the point of not trusting anybody but your brother... that could have twisted something in an already hurt child's brain... For me, it's just another interesting layer added by the fandom.