Originally posted by Texas KellyImpossible. And there's a very practical/"scientific" reasoning behind it.
In the Heroes world, as demonstrated both by Sylar and (to a much lesser extent) by Doctor Who, and as eventually rejected by HRG in the most recent episode, becoming evil involves developing a total apathy/lack of concern for others, to the degree where any feelings one has for any other person need to be completely shut out. This is completely contradictory to how Peter's power works - as Mohinder said, Peter is an empath; he must tap into the feelings/emotions of the other heroes he has come into contact with in order to make use of their abilities. Thus, were Peter to turn evil, he would be reduced to an average human being, because he would have to shut off the very mechanism by which his power works.
In short, Peter is quite possibly the only Hero who can't turn evil. I foresee a "Spider-Man"-style path for him down the road, where he is misunderstood and his wide range and strength of abilities make it easy for any manipulator to re-cast him as a menace to society in the public eye.
Did you miss the scene where he used his powers to screw with the future-painting guy? I don't know how anyone could watch that and think "No, this guy will never turn".
And I'm not quite sure how Peter would be using the powers of someone like Sylar based on your theory, since he surely has no feelings for a murderer. But if Peter has to tap into Sylar's feelings and emotions to use those powers, why can't that have a negative effect on him over time?
I couldn't imagine that I was the only one who made the "Lost" connection ... although I'm not sure I'd describe myself as one of the "screen-grabbing obsessives" either.