Sometimes it's just too difficult to be the bad guy especially if, as you say, quests give you good moral points for completing them.
In things like Red Dead, I was...pretty neutral. In games lke Fable 2, I play through as a good guy the first time then evil the second, just to see what I missed. Of course, this inherently makes it hard to complete the game as shop owners run away from you.
In Oblivion I played mainly as a good guy (although there wasn't exactly a moral scale) but I did love killing them guards every one in a while...just for the hell of it =D
But yeah, sometimes the developers make it more taxing to be a baddie. Sometimes they go too far the other way when giving a deserving gentleman a friendly slap in the face gains you as many evil points as eating a new-born baby kitten then pooing it out in front of a sickly orphan.
Not many games have the balance right yet, is the gist of this post...