. Define your character as you choose, mind you. But my characters act according to their own moral codes, their definitions of what constitutes right and wrong, though. I try to approach every situation in the game more like that, than to follow some strict definition of "being bad means I pick the red button".
That's fine as a starting point, but the Dark Side twists your perceptions, what was a reasonable but opposing viewpoint becomes unreasonable the further you go into the Dark Side. Look at Anakin in the Revenge of the Sith, his views are skewed, and as the film progresses they become more so, until any disagreement is answered with anger and perplection.
That is why the Jedi suppress emotion, any strong emotion can lead to a moment of anger, which lead to more moments of anger, and then your corruption.