Think about all the bad things people have done in history. Check out what slavery has done through out history. You're also basically killing indiscriminately. Being evil for evils sake. Dark Side 5 is that.
You're equating being evil with the dark side. There are similarities, but it's not exactly the same, but for the sake of argument let's assume ds=evil. We are talking about the Sith, who the entire emphasis of their teaching is that the dark side is better and where you should put all your focus. That's very different than comparing that to your average Joe on the street. The goal of a sith is get to dark side 5, if that's true then why wouldn't a Sith Pureblood be more proud of being white than red?