Let's let Abus Dumbledore (and Granger) clear this one up once and for all -- because every house thinks they're the best house, and every house is necessary if Hogwarts wants to thrive.

"Remember that comment that Dumbledore makes at the first sorting feast? He says, 'Nitwit, blubber, oddment, tweak,'" Granger said. "Those four words are what each house thinks of the other houses from their own prejudices. If you’re a Ravenclaw, everyone else is a nitwit. If you’re in the jock palace at Gryffindor, everybody else is blubber -- you know, they’re overweight, they’re not athletic enough. Oddment is what the purebloods in Slytherin think. And the last one is tweak, which is the position of the humble people in Hufflepuff... I mean, they’re proud of their humility. And so Dumbledore is saying right after the sorting, understand that you being sorted into houses already made you into little monsters. You’re already taking on these identities which are going to be the prejudices that shape your whole life."

Don't you see, guys?! We read these books from Harry's perspective, so when we're reading -- no matter what house Pottermore sorted us into -- we are all experiencing the world from the prejudiced angle of a Gryffindor. And Gryffindors, despite their do-gooder reputation and their heroic qualities, do not like the people in Slytherin.

Let's be better than those Gryffindors, then, and give the Slytherin folks -- minus Draco Malfoy, of course -- a fighting chance to prove us wrong. Due to the bravery of Severus Snape, Narcissa Malfoy, and that dang potions teacher, they at least deserve that much.