What makes this dangerous, like you said, is the fact that Harry seems to justify all this by saying to himself "I'm not in Slytherin. If I were truly Slytherin, regardless of my desires, it would have put me there. Therefore, in this society, I'm better than Slytherin," or something along those lines.

And who taught him that logic? Dumbledore. That man scares the piss out of me.

Hell, if you want to take paranoia to Moody-levels, you could always say that isn't it funny that Dumbledore's helpful Weasleys were just there when he needed them...

(Actually, on your line of thought about the logic of Harry being a Gryffindor or not, Kiri (ataniell93) and I sometimes RP back-and-forth this little Slyth!Harry timeline where Draco, who was horsing around going back and forth through the platform barrier, saw Harry again before the Weasleys could and--figuring he was Our Sort from the tailored robes at Malkins--helped him through instead. Kiri has a snippet of it, actually, in her journal somewhere.)