That kind of already happened when Dr. Octopus swapt bodies with Peter and became the Superior Spider-Man.

doom-wolf beat me to it, but I think it's his inherent personality. Like, I know it was a bad movie (that sadly started out with a lot of potential) but I think the scene on the rooftop where the films main movie grills him about his motivations ( "No. No. People WANT to win the lottery, People WANT to fuck Scarlett Johansson, No one WANTS to risk their life so some moron can walk through the projects at night..." ) and goes on to ask "what's the point of wearing a mask if you can't do anything you want?" and truth be told, he makes a lot of good points. I think it's just that some people are more willing to forgive, sacrifice, and do good than others, it's probably something that goes right down to the genes themselves, since some of the most privileged & pampered people can become the most vile of criminals, and yet the most downtrodden and betrayed forgive and even do good by those that wronged them even when they gain strong leverage which to seek revenge.

But he could have morphed into a villain since before uncle ben died, he was exploiting his powers for personal gain. I can imagine a scenario occurring that if Uncle Ben was instead diagnosed with cancer or liver failure or whatever instead, and his insurance screwed him over denying life saving medication for him. Being betrayed by society as a whole like that, and doing what was necessary to help his uncle, maybe he would rob some of those armored bank cars that seem to be everywhere in Marvel's NY, and would start to feel more comfortable spitting in the face of the law and society as a whole.

Anyways I think the "sinister 6" movie will have a lot more compelling storytelling and characters with more relate-able impulses and feelings than spiderman's seem to be. apparently the focus is on the villains which has never been done in a superhero movie franchise before.

*like I know kick-ass 2 was a bad movie*

damn I hate it when I stop typing and I forget a chunk of somewhat pertinent info that makes the whole statement seem weird :P