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I can't see why these violent thugs can't just be all shot myself, society would be better if all of them were shot.
If the same thing happened here in the U.S. and a group of armed civilians intervened, supporting the cops by shooting a few of those sonsabitches, the real tragedy lies in the fact that the cops would be ordered to arrest the armed civilians --
and they would!
But you are absolutely right. The very best thing that could be done if the refugees pull the same stunt here is gut-shoot the front rank, the rest would turn tail, vanish, and we would never see another such demonstration. But Obama, and every political suckass on down the line to the local police commanders would be screaming for the heads of the civilian shooters -- and the cops would follow their orders.
So abandon any hope you have of seeing anything as sensible and effective as civilian intervention in an aggressive refugee disturbance. You might see a lot of non-lethal stuff like water cannons and, possibly, rubber shotgun shells, none of which will serve to discourage repeat performances.
I believe a good idea would be to spray those entire crowds with an indelible skin dye containing silver nitrate, which is impossible to wash off or otherwise remove, then to start arresting and either deporting or imprisoning anyone who is found to be stained.
We've got to do something if these demonstrations start happening here, because if we don't nip it in the bud it will become progressively worse until we'll be experiencing what Europe is going through.