These questions arise from a much simpler point. Personally, I'm in favour of gun rights in America and also in places where it's practically a dangerzone with terror attacks happening very often. But this isn't the question here. The real problem is actually the immigration crisis. It seems like it's much easier to argue that guns could have stopped these attacks than to say that immigration control could have stopped them. The fact that the terrorists almost all came the same routes that the other Syrians come from -from Asia to Greece to France etc- shows that there is a real danger with the immigrants. There may be a lot of real refugees amongst the crowd (of which this is another point for different debate) but the risk of having real Islamic radical group having free passageway into all the countries of Europe is much too high.