Chewy, I hate to break it to you, but people, by and large, are stupid. And history is made and written by people. Therefore, history is chock full of stupid. Even scarier, a lot of highly concentrated stupid gets put into government, especially when people are angry and afraid. You only need to go back to 9/11/01 to see the truth of this. How many otherwise calm and rational people, after watching the Twin Towers fall, got the fool notion in their head that it'd be a great idea to turn the entire Muslim world into a glow-in-the-dark parking lot? (That means nuking the everloving drek out of them, in case you didn't catch that.) Hell, I was one of them! I can tell you straight up that if I'd had the launch codes on that day, I'd be guilty of more than a few war crimes by now. Your arguments are nice and rational, but they ignore the fact that people who are angry and scared aren't rational. Going back even further, you only need to look at Germany in the wake of the Great Depression. Germany had gotten the hammer dropped on it after WWI, and there were people starving and angry, but not knowing what to do. You take a guy with charisma, who can give people a clear target, and say, "This is your enemy! HE is the one who made you suffer!" and you'll find that they can get people to do terrible things of their own free will, charging blindly into the abyss.
People are terrible, stupid, wretched creatures, and sometimes all it takes is one bastard with an axe to grind or a personal insane grudge against a group, and all hell breaks loose.