There is one simple difference between the threat of Islamic terrorism and, say, other forms of domestic terrorism, ie: Irish nationalism, indigineous uprisings, the FLQ etc. And that difference is this: it is a choice to increase the population of Western countries from these regions where the terrorist organisations are flourishing. Those numbers have increased exponentially since the attacks of 9/11: a very poor public security choice when you think about it. 

It would make more sense to address migration needs from countries and populations where this is not a problem; in short, to take an evidence-based approach rather than an emotional approach based on short-term appeals for humanitarian assistance.