>>723868669
The game railroads you in many ways to do the NCR stuff, especially during your first playthrough, but again it kind of shows you how incompetent and how out of control things got in their hand. Literally the first mission you do in the game is the consequence of them giving a bunch of criminals access to explosives. And the ramifications of that effects the early game.
You're right: there is no guarantee years into the future there isn't going to be another conflict; Human nature is filled with it.
But giving the keys back to the Republic is attempting to play a Nation's greatest hits soundtrack on a with a really broken recorder.
Part of the questioning of siding with the NCR is 'Do you think that the USA, with every single one of its old world-like flaws, deserves another chance?'
You're in a post apocalyptic world now— the Patriotism hat has been off, buried, and forgotten at this point.
Now you have to really decide.