Tatsua Aiisen said
All of the houses have the potential to produce Dark Wizards, and all of their traits have the potential to be bad in certain ways. It's just because Slytherins are ambitious, so the dark wizards produced by their house are more likely to be well-known.

Yog Sothoth said
I understand that but jk Rowling wrote the slytherins as very bad, I don't think there was any slytherin student in the books that was portrayed in a good light, hell they were not even allowed to help in the battle of Hogwarts

Tatsua Aiisen said
Don't spread misinformation. It's just that, the series being focused on Gryffindor, Slytherin wasn't really paid attention to outside of the villainous characters. Which happened to be from Slytherin.

Yog Sothoth said
I understand that but jk Rowling wrote the slytherins as very bad, I don't think there was any slytherin student in the books that was portrayed in a good light, hell they were not even allowed to help in the battle of Hogwarts

J. K. Rowling stated in a PotterCast interview that some Slytherins were among the reinforcements brought by Slughorn during the Battle of Hogwarts.

PotterCast 131 J.K. Rowling Interview Transcript said
JN: And how much is it that being sorted into Slytherin is, you know, sorted into good guys and bad guys here?

JKR: Well, they’re not all bad, that would- I know I’ve said this before, (JN: Yeah, I remember.) and I think I said it to Emerson, they are not all bad, and, well, far from it. As we know, at the end, they may have (laughs) a slightly more highly developed sense of self-preservation then other people because…

SU: Yeah, right.

JN: Yeah.

JKR: A part of the final battle that made me smile was Slughorn galloping back with Slytherins, (SU: Yes!) (JN laughs) but they’d gone off to get reinforcements first, you know what I’m saying? But yes, they came back, they came back to fight, so I mean- but I’m sure that many people would say “Well, that’s common sense, isn’t it? Isn’t that smart, to get out, get more people and come back with them?”

JN: Yeah.

JKR: It’s the old saying, (SU: Just…) “There is no truth, (JN: I believe it.) there are only points of view.”