Oh I'm not too worried about it in my lifetime. We have a nice big ocean and a neighbour who agrees with what we are doing right now.You're more likely to die from a bathtub slip and fall. Sensationalism is turning you into a little scared man.
Europe however has to worry about the whole land thing.
Like I said. It isn't about them being Muslim as much as its about them being young single men, under or not unemployed, different cultural standards when it comes to misogyny, homophobia, and many other ideals.
Then with a lot of time on their hands, no real hope of improving their lives and a language barrier.....well that is about the easiest recipe for civil unrest, higher crime, and the locals turning against them creating a ghettoisd environment I can think of.