I can't really say which future is best for humanity, I can only hope the right side wins in the end.
If I can be deadass honest with you, I feel the same way. I don't know if the Legion is the best hope for humanity, or if House is, or NCR or pure unbridled anarchy. I don't know. I just found myself inexplicably drawn to the Legion; and when I talked with Caesar, something about their ideals clicked. Something I really can't put to words made me realize that I could honestly see myself siding with them; if only because I dared to believe that the Legion is capable of conducting themselves less ruthlessly in peacetime.
When I think about it, the idea that the Legion could be better than what has come before is the main reason I sided with them; something about them told me that they weren't as irredeemably evil as everyone says. Maybe you're right. Maybe the Legionary mindset is set in stone at this point, and the Legion will simply collapse in on itself. But I suppose I've accepted that. At this point I see the holes in the Legion philosophy, I see its flaws; but instead of turning away like Ulysses, they made me more eager to help them. To guide them along with Caesar into the peaceful neo-Rome that he has planned; to make a better future, with the "bad guys".
Do the ends justify the means? I really don't know. I can't say. I don't agree with everything the Legion does, just like how I can't agree with everything a certain political party does. All I can do is back the side I think offers a future, like you. And for reasons I wish I could explain, I see something bright beneath the banner of the Bull. It might take decades. Might not happen until after Caesar or even the Courier's death. Might not happen at all. But so long as I believe it can happen, so long as I keep explaining why I feel the way I do, maybe I can get other people to consider the Legion as a viable future, if only for a moment.
I don't blame other people for hating them. I can't. But when Ulysses says that there's no future "in the Bear or the Bull", I take it as a challenge. A challenge to see the good in the Legion, and at the end of Lonesome Road convince him (and honestly myself) that it won't collapse. To those it conquered, I'm sure Rome didn't seem benevolent. But after a couple generations, people in as far flung areas as Germany and the Middle East considered themselves Roman. It became a point of pride. Hell, the German name Kaiser is a derivative of Caesar; yet the Germans fucking hated the Romans until (and probably a while after) they were conquered.
The conquerors are always seen as the villains. The NCR conquers with diplomacy, and as a result we can stomach their imperialism more easily. But even though the Legion conquers at the tip of a sword, I still want to, still have to believe that eventually it can resemble Rome at its height. A massive empire, ruled justly (or as justly as possible) by (relatively) qualified leaders; an empire in which, after a couple generations, even people as far as Chicago can consider themselves Legion.
Except for the profligates in the Capital Wasteland. They're all getting crucified.
EDIT: I've just realized that we haven't really heard from any NCR profligates on this issue. If any would like to contribute, I'd love to hear about their viewpoints.