They've probably been watching CNN for the past few years.
We know enough about Islam now that we shouldn't expect muslims to act in ways that are rational or civilized by western Judeo/Christian standards.
But most of our "leaders" and media remain delusional about Islam and believe (or pretend to believe) there is some great silent majority of "moderate muslims" that are just like us and are waiting in the wings to be discovered.
The truth is that a "moderate muslim" is an anomoly way out on the fringes of the bell curve.
Helping a muslim is like feeding a poisonous snake.
The snake, like a muslim, may accept your aid but at the first opportunity will attack you because that is its nature.