I appreciated Victor Davis Hanson's reply to the same question. It was spot on:
I draw two lessons. First, that immigrants seeking refuge in the West must be grilled for their attitudes toward our civilization, our religion, and politics. Whether it be Somali refugees in the United Kingdom, Algerian ones in France, or Balkan ones in the United States (remember the Salt Lake City shooter in February, as well as four of the current six accused terrorists), individuals given the privilege and benefits of a new life then with some regularity turn around and attack their adapted fellow citizens. This unacceptable pattern has to be scrutinized to prevent future such atrocities.
Second, mercifully, terrorists can be counted on to make dumb mistakes. I established an honorary "Stupid Terrorists Club" in 2005; its founding members gained entry with such acts as having returned to retrieve the deposit on a van they had used to blow up a building, not wearing a car seat belt while transporting terrorist gear, or ordering $3,300 (in American dollars) worth of airline-related goods with an overdrawn credit card. This new group of six joined the Club by dint of its sending a jihadi DVD to a store be copied commercially and choosing as its target Fort Dix, a hardened military installation (among other components, it includes a prison).
The Fort Dix arrests raise the same-old/same-old script.
X-numbers of jihadists are caught trying to plot assassination, or to attack an airliner, or to take out a mall. They all will deny it.
Someone like CAIR will jump in, perhaps with the ACLU, alleging improper this and that; and the public after privately sighing relief and a few guarded grumbles along the politically incorrect lines of “Who in the hell let these people in this country?” will return to its normal state of amnesia.
And as long as these plots are not successful — or for that matter others like the recent Saudi effort to blow up an oil field, or those uncovered in Britain promising more killing — then we can have our hot-house arguments over whether we are really in a “war against terror” as we put scare quotes on anything associated with the notion of an Islamic threat.
But, if just one time, one of these plots succeeds and reaches a magnitude of 9/11 then the media will revert to form — suddenly dropping the “Bush took away our civil liberties” for “Bush didn’t do enough to protect us.”
And then, of course, the irony of it all can be seen in the profile of the suspects: Islamic terrorists from the former Yugoslavia, on whose behalf the U.S. bombed a European Christian country [thank you, Bill Clinton]; illegal aliens at a time when those who object to the immigration crisis are considered nativists; a former resident of Jordan, a country showered with U.S. aid. At some point, we see how insidious are the effect of Middle East ingratitude, and how the envy and hatred of that region permeates its expatriates, the more so the United States has tried to help them.