Oh, I agree with you, injate.
It's not just about the cold logic of whether or not attacks could be staged without the confusion of the mass of refugees...
It goes deeper, down to refusal to assimilate and imported cultural demands for things like halal food and Sharia Law.
If you read about England and Northern Europe (or have in the last 5+ years) they are dealing with some pretty messy stuff with this whole mass exodus and diaspora.