"When one party watches its own innocents killed by others, it may well seek revenge by killing innocents on the other side."

Which, of course, is why some Muslims seek revenge against the West. Western military forces have killed tens of thousands of innocent people in Afghanistan, Iraq, Libya, and Syria. In addition to that, Western governments prop up dictatorships in Muslim countries that kill thousands of innocent people, while oppressing tens of millions more.

It's completely understandable that some Muslims in the West would seek revenge for that.