What's the Moral of All of History?

In general all of history is a series of people saying well we need to pursue this truly grotesque mission because if we don't the enemy will or we suspect they already are. The only reason the enemy is doing it is because they think you're doing it and I'm sure there's a name for that paradox. After all what what thing could be too horrifying to use against insert enemy here Nazis, communists  or Muslim terrorists? That's always been the logic probably going back thousands of years. But World War I was a horrible nightmare because that logic leads to tens of millions of deaths.