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?
Of course being Dark Side is evil.
Killing lots of civilians is evil. In a war it might be seen as a nessasary evil, but it's evil none-the-less. Enslaving others is evil. And evil often times tries to play the "point of view" card.
Anakin became evil. He didn't have to stay a part of the Jedi Order. No one is ever forced into being a Jedi. If he didn't like the Jedi Order's rules, he could've quit. Instead he killed a bunch of younglings, and decided the best way to save everyone was to enforce his desires onto everyone.
Dark Side 5 is all about showing power over others every possible way. Dark side 5 is pure evil. Even if it leads to the easier path of great power.