Much has already been said and more will be said about the implications of yesterday's attacks in Paris. I don't have much of substance to add, but allow me to work though my thoughts.
It would be nice if the world were black & white, and we could filter the bad guys by their chosen god. But one needn't look far to find Muslim pacifists or warmongering Christians, Jews, atheists, and even Buddhists. But, of course, mankind's violent tendencies are complex, and choosing who to hate is not a path to peace.
The English-language recruiting publication of ISIS provides a helpful framing for my feelings.
Eventually, the grayzone will become extinct and there will be no place for grayish calls and movements. There will only be the camp of īmān versus the camp of kufr.
Their "gray zone" is the place of tolerance, which they believe has no legitimacy. They are quick to point out that this worldview is not theirs alone:
Bush spoke the truth when he said, ‘Either you are with us or you are with the terrorists.’ Meaning, either you are with the crusade or you are with Islam”
We are at our best in this gray zone.
One of the things I've come to appreciate about the Netherlands is gedoogbeleid (gedoog "allow, permit" + beleid "policy"), which is often translated as "the gray area." It describes activities that are formally prohibited, but not enforced. With this concept, even when treaties or cultural whims require that recreational drugs, prostitution, or euthanasia be illegal, the Dutch government can formally choose to tolerate activities they deem harmless.
This sense of "I do not approve of your choices, but I will tolerate them and welcome you into my society" is a gray zone. It is here that we are civilized and may coexist while sharing in the fruits of functional society.
ISIS, Donald Trump, and Geert Wilders thrive on sorting the world into black and white. I am afraid of them not for my personal safety, but for the risk they post to our gray zones. (For some hope, see also this map of nonviolent opposition groups in Syria and the writings of Nader Atassi.)