There are plenty of Slytherin that did not become a Death Eater. Plenty that went on to lead normal lives, running a quill shoppe, selling robes, working for the Ministry. I don't think that being a Slytherin sets you up for failure. Hell. Look at Slughorn. He was head of Slytherin house and he has done well for himself. He knows Gweong Jones of the Holyhead Harpies.
Actually it was never really confirmed that none of them stayed for the battle. I test Slytherin 95% of the time (the other 5% Ravenclaw). There is no guarantee that /all/ Slytherins are terrible humans. I am a slytherin and I fucking own it. I've got a tshirt with the motto and socks to match.
JKR only LET us see the bad in Slytherin to progress story lines. I cannot, nay will not, believe that pre conceived notions of the traits from your house in school will stop you from living a full, productive, happy life. I am proud to be Slytherin.
@dr_richard_ew
While we're waiting, can I ask who's calling?