From the Fallout Wiki:
"RE: Caesar’s Karma being neutral: I believe at the time my rationale for that Karma setting is that Caesar is in a Mr. Kurtz-like state of unmoored morality. Whatever moral framework he had as Edward Sallow among the Followers has disintegrated after years of being Caesar. I.e., it’s not so much that his Karma is neutral as much as it is alien. That said, I don’t feel strongly about that designation and largely feel that the Karma system was vestigial in New Vegas. If we’re trying to encourage players to form their own opinions about factions and individuals, having a design layer that assigns (essentially) alignment is weird."
"I'm sure individual players might want to engage in ranking atrocities -- something I've never really found was productive in discussions about history -- but Caesar and his crew in the same league as other brutal warlords. He was inspired (on our end) by people like Charles Taylor, Timur, and Simon de Montfort (the crusader). "Caesar" is a persona he adopted, but he effectively operates as a warlord with no regard for individual human lives outside of how he can use them."
I think Josh Sawyer confused karma with alignment.
part of that is that the whole faction is half-baked because it was rushed to release. Legion got the most cut from it, multiple towns beyond the Colorado were scrapped. And siding with the legion locks you out of a lot of other quests, so why bother?
Even if it's half-baked, I think the foundation of it is pretty repulsive especially the slavery and cultural annihilation point is pretty repulsive to a lot of people ethically.
And honestly, I'm glad its half-baked because if we got "civilian" settlements showing the Legion as "Being Safe and Prosperous" despite the slavery, mass misery, and cultural annihilation that they commit, a lot more Fallout fans would've been fascist trash (See: Enclave fanboys)