It did bother me in the Harry Potter books that Slytherin was depicted as the "Evil House." Which does make me wonder. The series is 3rd-person-limited through Harry's POV, so we only see the world--and Slytherin--through his eyes, so it's likely he's prejudiced and has a very anti-Slytherin bias. But then there's the tale of the Four Founders, and only Salazar is shown as ZOMG EVIL MUST HAVE PURE BLOODS and the one being most rational, and Gryffindor is heroic and never wrong, etc. that makes me uncomfortable a bit.

Which also explains the lack of insight on Ravenclaw and Hufflepuff, which still frustrates me. :/