This is an unusually horrifying act of terrorism. Ordinarily, we are accustomed to seeing terrorists do their own work. Those they recruit for suicide missions are not, as many studies have shown, religious zealots, economically deprived, illiterate, or mentally unbalanced. Instead, they are like grass-roots political activists who are willing to use extreme means to achieve their ends. But sending two mentally disabled women seems “demonic,” as some U.S. officials put it to describe a particularly repugnant form of terrorism that crosses all the red lines.

Interestingly, an incident like this forces us to think hard about terrorism. If some forms of terrorism are demonic or particularly reprehensible, it seems that other forms are more acceptable. Some cross the red lines, others stay within certain boundaries and are, to some extent, tolerable or at least understandable. Former Israeli Prime Minister Ehud Barak once declared, “If I were a Palestinian at the right age, I would have joined one of the terrorist organizations.” Barak is saying what many people think: I may not agree with terrorism, but I can certainly understand the motivation that leads those to join terror organizations.