Firstly, these are mostly teenagers in caves with yesterdays cell phones. They simply don't have the resources or the numbers to kill millions, or even tens of thousands. I don't think you understand that your argument is a purely emotional one[1]. It appears to be rather simple to sneak a firearm on a plane[2], and yet there has not been any repeat attacks like 9/11. Firearms are illegal in Paris and they have large divisions of domestic and foreign spies, that failed to prevent anything[3]. Now lawmakers around the globe want to outlaw prime numbers (encryption) yet terrorists don't seem to even bother using it[4]. Emotion aside, dollar for dollar, fighting malaria is more effective in preventing the loss of human life than fighting terrorism by many orders of magnitude.

[1]"If a man is crossing a river And an empty boat collides with his own skiff, Even though he be a bad-tempered man He will not become very angry. But if he sees a man in the boat, He will shout to him to steer clear. And if the shout is not heard he will shout Again, and yet again, and begin cursing - And all because there is somebody in that boat. Yet if the boat were empty, He would not be shouting, and he would not be angry." - Chuang Tzu

[2]http://www.huffingtonpost.com/2015/06/01/tsa-fails-95-percen... [3]http://www.cnn.com/2015/11/18/europe/paris-terror-attacks-in... [4]https://bgr.com/2016/03/22/paris-attacks-iphone-encryption/