There are 2 reasons you don't see that type of shit over here as much. 1. We don't have the slums they have in Germany and France that are basically a cesspool for these radicals. 2. We have a better intel, and police our own much better. We still have some slip through the cracks but it seems like Europe is having some sort of terror attack every week.
Sheer numbers make a difference. And we do have comparable issues with gang activity in certain cities where those same problems exist. I have no doubt that if a large number of refugees were allowed in, housed together (or not), they would find a way to kill Americans.
Yeah they would but I don't think it would happen as frequently as it happens in France or Germany or Turkey.