Every day it seems that the threat from the Islamic State extremists grows nearer and more credible. Earlier this month, Geneva was on high alert following reports of militants in the area. The furor in the United States has been mounting in the wake of evidence that the two individuals who killed 14 people in a mass shooting in San Bernardino, California, had pledged allegiance to the group. That atrocity followed the series of attacks in Paris in early November that claimed 130 lives.

These horrific acts of terrorism must be condemned and the victims and their families offered our thoughts and prayers. The radicals must be confronted, contained and destroyed. But anger must not give way to over-reaction and the excesses that will give the group the "war of civilizations" that it seeks. This is not a war against Islam, or even against conservative Islamists. Our fight is with the murderers and terrorists that act for or with the Islamic State group.

It is tempting in the face of such inhumanity to give into fear, and to respond in an excessive and heavy-handed way that accepts "collateral damage" — the killing of innocents — as a sad but necessary consequence (and, to be fair, just retribution for the killing of equally innocent individuals by the Islamic State radicals). The calls by some in the U.S., for example, to ban Muslims from the country and to deny them their constitutional rights is on a continuum with the reaction by some in Japan — to disengage from the Middle East — after the group beheaded Kenji Goto and Haruna Yukawa. In short, we cannot let Islamic State set the terms of engagement.