The problem is exactly the "how", as you described. And personally, I don't really have any idea, since all the possible ways seem to involve somehow contradicting that goal "temporarily" (by using violence, limiting individual liberties, etc.), which I don't like. I think maybe over time, (a very long time, perhaps?) the way of thinking of human societies will slowly (and through a painful process) shift to that direction (and maybe not! who knows!).