well, he was seduced by the darkside. besides, it would still be a conscious choice to turn. Seduction merely means he was tempted by the power and possibilities of the dark side. It's still a conscious decision whether to give into that temptation or not. I know my choice of words might not have been perfect, but the idea was never that he believed the dark side, or the emperor, to be good. He made the choice to be a "bad guy" & knew it. When i say that he believed in the emperor, i mean just that. He believed in the power & the teachings of the emperor. Vader didn't see himself as a pawn, but as a loyal disciple of sorts. He trusted his teacher. Nowhere does that imply he was tricked into being evil. that was his choice. where he was tricked was in believing that the emperor actually cared about more than what Vader could do for him. That he actually cared about Vader & his progress, etc. etc. I'm sure Vader expected to be the emperor's heir, so he was essentially a father figure. It's when the emperor told vader to kill his own son that he began to doubt his master. after all, if the emperor would have him kill his own son, what did the emperor really think of him? Was Vader disposable too? surely not! But he get's his final confirmation of this in the throne room in ROTJ when the emperor commands Luke to destroy his father & take his place by the emperor's side. That's when Vader finally knows that he really was just a pawn. & that's when, with the help of Luke's compassion and faith, he is finally able to overcome himself and turn back to the good side.