My Shepard is neither a hero or a villain. He does what it takes to get things done. Simple as that.
Conrad Verner is perhaps the best example of this. Chris Shepard really doesn't want any fans because he just sees what he does as necessary. He's not trying to be a hero. But he'll put up with it (the autograph and picture) until it goes too far. When Conrad suggested becoming a Spectre, Chris couldn't take it anymore. Conrad wants to be a Spectre because of mere idol worship. With that serious of a job, that was unacceptable. So he was blunt - he put his gun in Conrad's face. Conrad probably thinks Chris is a villain now, with the way he ran away crying. The way I play Chris, he probably felt bad for a few seconds, but knew it was what had to be done.
He's a renegade for all of the above reasons. But, again, he's far from a villain. After all, Chris would give his life to save the universe. It's his job. And he will NOT accept failure.