"Good" and "Right" aren't Light side. A Buddhist/Zen melange of 'all life is beautiful and all creatures deserve life' is Light side. Just as Dark side doesn't mean "I'm just in it for me", it means 'I'm in it for me and I will cause others suffering and pain (and likely snuff out their life) whenever I feel like it'. The truly powerful Sith will be mostly dark with some light simply because that way lies more power, but add a healthy dose of paranoia. The truly potent Jedi will be mostly light with a tinge of dark simply because sometimes the "right" thing to do for the safety of others is to kill someone. However, following the Light side means that you don't get to make that decision. That's the universes choice, not yours.
*shrug*
I honestly laugh when my pure Dark assassin makes some choices as it comes off like she's a raving psychopath.