1) Everyone owns the means of violence. This seems good from an equality perspective. The issue is that the capability for violence is at an all time high that if everyone gets an assault rifle, a tank, a missile silo, etc, then all it takes is a couple of crazies to end the world.
2) Only some own the means of violence. If the group that owns the means is well trained and has oversight this is a relatively good option. The issue is that when one group gets the power, they like to keep the power for themselves and keep everyone else down. It's a human nature thing and human nature is a hard habit to kick.
3) Nobody owns the means of violence. This eliminates the potential destructive capabilities and brings everyone to an equal level which sounds nice. However convincing everyone to get rid of their weapons is unrealistic because again, there are currently groups with the power and convincing them to give up their power isn't going to happen.