As someone posted before, it is hard to see things here as good or bad in the contest of jedi or sith. Yes, we can all agree that Sith Empire is based on terror and oppression, but have you played trooper or smuggler? His story begins on Ord Mantell, under "Republic" control. I used quotation marks on purpose. Republic supposed to stand for the good and noble things. But do ANY quest there, they will want to charge you for breathing. And did you notice a little difference between Imp and Rep IF? There are no doors on shops on IF.
You are playing character who strongly believes in the soul believes of your own side, on the basic ideals which probably only exist in very few people, and you want to do whatever is necessary to see your ideals come true. You caught a criminal but your justice system is slow and corrupted. What can you do? Who you gonna call? Noone, just take your lighsaber and make a shish kebab out of him cause he is destroying the picture of your ideal republic. You fight corruption any way you can and know, with your lightsaber. I wouldn't say that because of that your dark side jedi is a bad character.