Try to play full dark side SW and you'll see how vrutal you can be. For example: !!!SPOILER!!! At the very beginning of the story, on Dromund Kaas you can Kill a Sith/ or his wife and child. If you killed the sith, you can sleep with his wife and make Vette watch, then Darth Baras will congratulate you. And it is only one example.
Ppl play for the Empire beacuse THANKS GOD we are able to do this. I mean in movies (especialy with disney), other games we act like or see a jedi or another good guy again and again. And everything is similar and boring. If you play for the Empire it fells more real and gives you emotions.