It is an experiment. Our lives are traded for that experiment. They really do not know if, at some point, the fast-growing population in the West will settle down, integrate and not commit acts of terrorism. But in the meantime, the deaths pile up of innocents, just young people out enjoying themselves, thrown to the wolves by their politicians. 

Reports from Britain's Parliament, when they were eventually attacked, did not show brave politicians confronting the terrorist (the police had to do that) but politicians cowering in rooms and under desks, a prime minister hobbling around in her high heels unsure where to run to. The courage of the sound bite meets the fear of reality.