[Ginkasa]

Its not like that. Unlike something like Fallout or Elder Scrolls or even other Bioware games like KotOR or Baldur's Gate, Shepard does have a little bit of pre-determined character. That character is, without debate, all about saving the galaxy from the Reapers. He is always the good guy, no matter what the player wants. The player just gets to choose whether he's nice about it or whatever.

When Shepard chooses the not help someone its because he's looking at the greater good. He's saving the universe, NO he doesn't have time to stop and decide whether to give your baby genetic modifications or not. If Shepard decides to ruin somebody's day its because either a) that person is the enemy and NO MERCY b) its for the greater good (dropping a nuke or prevent and deadly invasion) c) Sir Isaac Newton is the deadliest son of a gun in space.

Shepard is never looking to take over the Reapers and wreak havoc or destroy Earth. I know this because Shepard makes this very clear throughout the games no matter what choices you make. The player may want to be an evil overlord and kill everything, but they can't do that in ME. The player chooses how Shepard goes about saving the universe, but not why and certainly not whether he should or not.