carnival-phantasm:

Does anyone actually side with the Legion unironically thinking “Yeah, I’m a hero! I’m doing what’s best for the Mojave”?

Yes. The major constraint on society at that point isn’t lost technology or scarce resources, but that what capacity exists can’t come together in a mutually supportive network because there are bandits on the road and settlements are only tenuously connected by brahmin caravan.

“The Roman Legion” is a known social technology which can be operated at scale to pacify trade routes, which is exactly what the world most needs at that point. The NCR’s Ranger patrols can’t sweep hard enough, and its city-state federalism would splinter before it extended far enough anyway. Meanwhile “a particularly strong Las Vegas Strip” doesn’t seem useful at sufficient scale.