But your scenario is absolutely plausible. Fortunately the number of sick minds out there who would actually carry out such an attack are few in number or are stupid enough to get caught.
Technology can be a frightening thing in the wrong hands.
Life is struggle. And people who feel they have little to live for in a certain society tend to create a place for themselves in a new one of their own making. But to make an omelet you have to break a few eggs. I don't get into all of this moralism that I've been reading out here about the good and bad of terrorism. People will use terror whenever they think they can get away with it.