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.
I will disagree with you on thing: Not every darkside option in the game is considered "evil" and not every lightside option is considered "good."
Like....on Ord Mantell. the kid that you go find in the separatists base thing, you get darkside points for telling him to go back home, to be with family. While on Dromund Kaas, you get lightside points for killing the slaves at the Colossus.
Not everything in that game is that black and white.