It's actually a win-win-win -- the psychotic a-holes avoid vengeance because, after all, they're lunatics. We don't want to punish people for being crazy. They simply can't control themselves!
The result of all of this is a world run by psychotic a-holes. We are supposed to cater to them, so as not to offend their sensibilities. We are supposed to avoid vengeance, since they're not responsible for their actions. And we're supposed to give them anything they want, to keep the nuts happy.
These people aren't nuts, though. They're evil, and they're opportunistic. When they see weakness, they strike. It's as true for everyday criminals as it is for Islamists around the globe. We cannot surrender to any of them. But our president already is.