I'd rather deal with retarded buereaucrats than efficient governors who will throw me into a cage to fight to the death for their amusement.
I realize now that it seems like I'm trying to justify the legion actions. That was not my intent. They clearly do the worst stuff overtly (the NCR does shitty stuff like the legion too, they just hide it). It's just that in my playing a legion-aligned character, Caesar and company have (bad) rationalizations for what they do. When I think of "evil", I think of someone being terrible because they want people to be in pain and suffer, and less because they believe their actions are necessary.
Most evil or imbalanced people believe they're perfectly justified in their actions, even if the justification amounts to little more than "they started it" or "I deserve better".
The legion tries to mimic an ancient system, back from when people had very different ideas about morality and having the state impaling thieves on the side of the road was just a fact of life. So for us and most people in the Fallout timeline, they naturally come off as evil. Like Metro says, the game didn't explore much (if any) of their positive side. You are told their areas are generally free of criminals, but since you spend most of the game being pounced by raiders it might as well be some random codex entry like in Dragon Age where you get detailed accounts of the Qunari society that you never see.