My instinct when I saw your headline was "I would use it to make money." It's completely selfish but that's where my gut tells me to go. Thinking a little more about it, I think it's because I believe that if you went back in time and killed Hitler, you'd have some other Nazi asshole there to take his place. Hitler was a symptom of a societal shift at the time, not the cause. I think saying otherwise gives a little too much credit to the "leaders" of such movements. I think they're just lucky. Looking out for your own interests would be the only way to control the future you want to see. It's just like that saying from Gandhi, "Be the change you wish to see in the world."