In Chapter 3 of "Life, The Universe and Everything", Douglas Adams immortalized the idea of the "Somebody Else's Problem" field, which makes things invisible. We all tend to look at the world of politics and war through an S.E.P. field. This has to stop.
Consider the problem of Islamic terrorism: most non-Muslims feel that it is the responsibility of the majority of sensible, peaceful, moderate Muslims to "do something about" those who perform hate crimes against innocent civilians in the name of Islam. And yet when a Muslim woman is violently attacked by "patriotic Canadians" for the crime of wearing a veil over her face, we dismiss this as an act of deranged idiots -- not something we'd do, not something we condone, so not our problem. But it is our problem.
Conversely, when sects of fanatic Christians raise money to bring on Armageddon, or disrupt the funerals of soldiers, most Christians dismiss them as "wingnuts -- not real Christians" and hence S.E.P. Wrong! When people who call themselves the same thing you call yourself do something despicable, you have three ethical choices: convince them to stop, have them officially expelled from said tribe, or withdraw from the tribe yourself. The collective is responsible for the acts of its individual members, and vice versa. That's the social contract.
I know, it's hard enough monitoring our own behavior without worrying about that of others; but in today's world it is not enough to simply "set a good example". Each of us has a responsibility to engage those we regard as "deranged", find out why they think the way they do, and try to talk them out of it. We may not succeed, but we must try; otherwise nothing will halt the condensation of a diverse society into mutually hostile pools of like-minded individuals reinforcing each other's prejudices.
Talk to your enemy. It's no one else's problem.