The Legion bringing 'the rule of Law' to the wastes is only good if their subjects are actually better off under that rule then they would have been without it. I've seen no evidence that anyone anywhere actually benefits from being a Legion subject except perhaps Legion soldiers. The people were getting by, and some even thriving, in the "lawless" wastes before the arrival of the Legion. While it is obvious that what passes for Legion 'order' is more brutal and oppressive than the alternatives, what makes anyone think it makes it's subjects any better off than they would be under the NCR or independent? Sorry, I see no good at all with the Legion because the cost of their 'law and order' comes at the expense of other superior options for achieving the same.
We have no idea what life is like for the actual citizens of the Legion, considering all we see in New Vegas are the military forces. We never encounter an actual Legion village, town or city. What we are seeing are the folks who are in the path of their expansion. From what we know, the territory controlled by Caesar is safer, and they seem to do pretty well with the traders. Perhaps tribes that fell under Legion control earlier have it better? We can't say either way.
Who the heck said 100,000 population?
You must be reading the wrong post.
"Big" is probably 700-1200 people in Fallout, After bombs dropped.
700-1200 may even be pushing it...