Indeed, Islamist fundamentalism is not only a risk factor. It is the risk factor, the common denominator linking all the great terror attacks of this century — from 9/11 to Mumbai, from Fort Hood to Times Square, from London to Madrid to Bali. The attackers were of various national origin, occupation, age, social class, native tongue, and race. The one thing that united them was the jihadist vision in whose name they acted.He overstates slightly. Timothy McVeigh wasn't Islamist nor was the IRA so perhaps Krauthammer should have said "almost all" instead of "all.
The America-haters at Salon have taken great offense at Krauthammer's thesis; their critique of his argument is here. Note that they believe the U.S. is responsible for all Islamic violence. I suggest you look at both articles and make up your own mind.