For nost Slytherins, their parents were death eaters. THey had a choice: Fight against my freinds or my parents? I know in my case, I would rather ahve family over freinds. If they didn't fight at all, they would be sought after by the Dark Lord and killed afterwards. Thats just something to think about. Most of these people didn't nessasarily have loving parents, they wern't exactly taught right and wrong, you know? I just wanted to say this because I am a Slytherin, always ready to protect my house.