I think he showed how anyone can view themselves as just doing their job, and he was good at it. I think it is left to us to wonder when he realized that he was an oppressive formce instead of security. He humanized the empire, that they are normal people who think they are truly helping, and it's usually not until they're so far in that they realize what they've been doing.

So is he evil? Depends on whose viewpoint. I bet he thought he was helping, up until close to the end. Andor does a great job at showing us that facism isn't something that happens overnight, it isn't something most people even realize is happening. It's insidious, slow, and you may not know you're even a part of it until your part is done. I think that's the true power of the show.