I find that a weak justification for shallow writing. Like the writers couldn't think of a system beyond liberal democracy so they imagine a group that does genocide and slavery and think that's clever. Or just a capitalist with a soulless machine army.

Caeser legion type factions only work in post Apocalypse settings (like the super mutants in Fallout 1 who were better written because the goal of that game was to survive in a wasteland not meant for humans) but New Vegas styles itself as a post-post apocalypse narrative about imperialism so groups like the legion are borderline harmful. There were plans to more fully flesh out the faction by being able to go to their settlements so I think there's a possibility that the caricature of fascism that liberals dream about wasn't going to be in the final game.