Everyone is forced to be a slave, not just women. Caesar's reasoning for not having women as soldiers is that he considers them more useful back home because they can have children, and are used as educators, if I remember correctly. He considers the soldiers to be expendable, and the women are not. This is portrayed poorly throughout the game, as you only learn this through some dialogue with specific people, as you only ever get to interact with their invading military. It would have been better if you actually got to visit Legion's homeland. Caesar also expressed desire to change the way things worked in the Legion after securing the Dam. He views the current state of the Legion as an unfortunate necessity to secure their survival until they have the Dam and are completely secured. In the Legion ending where Caesar's alive, it's shown that they start to calm the fuck down, just not completely, as their hasn't be enough time to completely change yet. This doesn't justify the Legion, and there's the possibility that Caesar's successor won't feel the same about change, I just believe that despite their many faults, the Legion has more potential than the NCR, which I believe is doomed to fail.
I'm not arguing who would last longer I'm arguing who is more blatantly evil. And the NCR is no where near as evil as the Legion.
Also they are completely against technology which is just a stupid primal fear that would probably kill them in the long run.