The Legion doesn't really make too much sense to me.
They are repeatedly described as a roving army- Ceasar says that he wants New Vegas precisely because it would give him a Rome, a power base from which to build his empire.
Yet, at the same time, they can apparently keep the peace in three State's worth of territory (which is, what, the size of France or something?). In the ridiculously dangerous Fallout world. When most of their soldier are goons with machetes. With no organized logistics or system of laws or solid economic backbone to speak of, beyond roving traders. This same Legion also has vast amounts of manpower, despite its nigh on primitive technology and refusal to use medicine more advanced than healing powder (if you aren't Big C that is). Since apparently everyone in the territories they conquered are primals who couldn't defend themselves, while the West Coast is filled with factions that could put up a good fight, even if not defeat the Legion outright.
The whole ''oh, but they can actually can keep the peace in their territory!'' seems like a pretty big cop out, a way to give some light to a bunch of roving rapists and mass murderers led by a delusional manchild.
As for NCR territory being a sea of lawlessness, the Mojave is a war zone, not their heartlands. If the NCR wins, the ending slides are fairly optimistic and show that the region stabilizes and prospers. Goodsprings, Primm, Novac, the Kings, the Followers, Freeside, heck even the BoS can be alive and kicking under their watch. Little indicates that the region faces imminent collapse. And anyway, it's kinda funny that people say that, because one of the very reason that the NCR cannot spare troops to deal with Fiends and bandits is because they use so many soldiers against the Legion.
Which IS an idiotic move by Oliver, don't get me wrong, but when one side has machetes and the other has freaking Vertibirds and power armor, you pretty much need to have the latter display ****** poor leadership to give the former a fighting chance.
And finally, it's not a dichotomy between NCR and lawnessness and Legion and perfect paradise of security (provided you're a young man). Most towns in New Vegas fare relatively well, Vegas itself is hardly a cesspit apart from the Fiends, and the only three times we see or hear about a town actually get attacked are Nipton, Searchlight and Bitter Springs. All of which are attacked by, guess who, the Legion. The one possible exception are NCR-hired mercenaries threatening Jacobstown.