The battle of light vs dark and good vs evil will occur regardless of the light/dark alignment of the character. Always picking light or dark options, while perfectly fine, does not capture a very complex character. This game has tons of story. It is supposed to give you hard decisions, evoke emotions, and make you really choose. If you defeat a bad guy, you can either let him live or kill him. Sure, he's valuable as a captive... but he's a monster, too. The grey character internalizes the struggle and acts based on character traits, rather than a predetermined alignment. "Pure" light and dark characters are, simply put, boring.
If anything, remove all indication of character alignment gains until after the quest is turned in, and randomize the (terrible) "good option always on top, evil always on bottom" conversation options. Make people actually think.