But, if we're going to be intellectually honest, it is undeniable fact that some groups are more likely than others to do certain things, in this case terrorism against Americans. In today's world, is it most likely that, when a terrorist incident from without against Americans happens, that Mongolians will be the perpetrators? No. South Americans? No. Finns? No. Namibians? No.
Middle Easterners? You bet. To deny that is simply hiding one's own head in the sand. That's correlation, and has earned it's need for additional caution.