FNV's story and characters are well liked because the they don't use their villains as cartoonish parodies of ideas they don't like.

Caesar is evil.
The society he built is a horrifying monstrosity.

But, he'll take the time to walk you through his reasoning, and it basically comes across as if he's forging the Eastern Tribes into a single use weapon.

He wants to take that weapon, plunge it into the rotting husk of the nation he was born into, and then arrange for that clash to force a new, superior society into existence.

The major, and obvious problem with that plan, is that he's treating the Hegelian Dialectic as a physical law that overrides human behavior at a societal level.
Yet, it's still compelling.

Furthermore, when people say things like: "he's kind of right though", they don't typically mean about everything. Caesar's comments about the rot in NCR society are right, and even NCR characters don't disagree.
It's just that identifying a problem accurately, doesn't make your solution any less horrible and ineffective.

There is a bit when Raul (the only guy that is neutral towards them) explains that while the Legion is terrible by itself, Arizona was so bad that you couldn't move around without the danger of tribals, raiders and looters. Until the Legion put order in there.

"I don't really have a problem with them. People around here tend to see them as invading marauders planning to burn and pillage the countryside. But I've been to Arizona, boss. Before the Legion, it was a nasty place, so thick with raiders you couldn't trade with a town two miles up the road. Caesar's laws aren't nice, and their actions aren't always pretty. But then, neither am I, but you keep me around."