I wouldn't call them not dangerous. By acting on their own they are much harder to catch. If they ever stop thinking in terms of bombs and just get a rifle and start shooting they could do lots of damage. Instead they have to go the complicated way, but they aren't smart enough to figure out how to make bombs so they gotta have help, and that's how they get caught.
But, some of these guys aren't so independent. Some make trips back and forth to muslim countries to learn how to make their own bombs. And , that's how they get caught.
They're all just innocent little babes.