But he does - or at least did - talk the talk of idealism really well, and while a Slytherin would probably try that if they saw the possibility of political gain, I think their basic insincerity would come through. I mean, just imagine Richard Nixon giving an idealistic speech about hope, joy, and world peace. He'd probably gag on his tongue halfway through.

Hmm. I think idealism in the Hogwarts houses is something I need to think more about. It doesn't seem to be something JKR was really interested in - Hermione's crusades are pretty much played for laughs - so there's not much to work with.

Maybe separating the Gryffindors & Ravenclaws is part of an underhanded scheme on the part of the Hogwarts founders to ensure that idealism never picks up steam and thus preserve the status quo, because I think idealism is a very Gryffinclaw trait - it requires both courage and intellect - but the way the houses are set up, no one socializes with people outside their house too much.