It's not irrational fear at all. It mightn't kill many people, but would cause absolute chaos.
A decent dirty bomb would make for one hell of a cleanup job. The substances are highly toxic and when vapourised in an explosion could be carried for a decent way.
You don't know what you're talking about, and shouldn't be so flippant about it.
In fact, I don't know why the hell you bother trying to talk this down, or say there isn't anything to worry about. IS are a worry, but more of a worry is the radical islamist movement all across Africa and the Middle East, and moving into Europe and parts of SE Asia as well. Thousands upon thousands of people are being terrorized, murdered, kidnapped, tortured, etc etc and you come on here, trying to tell us that it's not such a big problem?
You need to wake up, grow up, and look around at what is happening in these regions.
