Exactly. As terrible as the legion is, if they were to win and become the dominant society, they would seem GREAT for the benefits they bring; and the NCR and Vegas would be "evil" for their depraved excesses, negligence towards common people, and extreme self-interest.
You've got a point in that the dominant thought is the de facto norm, but philosophically, there's the question of subjective good vs. objective good.
For one thing, I don't see why you're putting NCR and Vegas in the same category there. NCR are obviously at odds with House, even though some of the "joes" are prone to excess.. the higher ups clearly have plans for the strip. Gambling and drinking clearly isn't part of their agenda. House, on the other hand, all he really cares about is his own power. He doesn't want to hurt anyone, but what he cares about most of all is his own privacy, which, as it happens, is only afforded to him by the greed of the commoners.
So, the way I see it, House (and therefore the strip as a whole) is kind of a non issue. He would rather the whole world went on without him, so long as he can remain where he is. His objective is to maintain the relative stability that already exists.
NCR is the US Army. The guys fighting the battles are only in it for the "good of the country" because it's what they believe a man should do. Fight for what's right, and all that jazz. I don't really need to elaborate on this, except to mention that it's also rooted in the idealistic 50s cold war mentality, where cynicism had not yet reared its head fully in American society. (There are jokes about it, sure.. but that's where the satire comes in. The jokes are for us to get, and not for the in game characters to comprehend.)
The Enclave is obviously the US government. Their primary tool is propaganda, and most of what everyone thinks and does is influenced by them in some way. They only flex their muscles, however, when their backs are against the wall, which really shouldn't be as easy a task as it was in Fallout 3. These are the people with no names. They believe in truth, but they feel like they're the only ones who are privileged enough to know what that truth is.
The Legion is the 1950s American fear. Call it Communism.. the Red Menace.. whatever. It's the bogeyman. Nowadays, it would be Al Qaeda. These guys are straight out of the bible. Death and destruction wherever they go. They have no king but Caesar. Even when he's dead, his will is law. There's no rhyme or reason. It's only because it is the will of Caesar that it is done. Ave.