The reason why casualties are so "low" at CHernobyl (although if you were one of them, or their relatives, you might not be so casual about it), is that the whole area was evacuated and exposure ceased.

If people had continued to live and work there and eat local food, they would have accumulated more persistent radiation damage.

The question, IMHO, in the case of a dirty bomb attack, is "How much of our infrastructure will we have to abandon, for decades, or even hundreds or thousands of years?"

In the case of 9/11, the area of a large city block or two was destroyed - its use denied for a few years while clearance and rebuilding took/take place. If a few city blocks of NY, or London, or Moscow, or San Francisco were rendered unsafe to inhabit for decades, there would be a profound economic and psychological shock.

Imagine the scenario of the Statue of Liberty emerging from a waist-deep concrete sarcophagous. (not a good analogy, because it's already been overused in "Planet of the Apes" and "Day after Tomorrow" and anyway, it's on an island out of the way.

The White House or a major government building would be a bad target, because there's too much open space in the Capitol, so you don't get much with one hit, but what about Wall St? Or the Downtown business centre of a major US city?

Imagine having to build a new highway system to cut off and bypass the central business district, and re-route all business and traffic to satellite centres.

Many people would choose to leave that blighted city, rendering it economically stagnant and potentially decaying and crime-ridden.

Perhaps the threat IS in our imagination, but that's because we very much CAN imagine this scenario.

If the danger is not of this magnitude, then some serious reality needs to be injected into the situation, by discussion and analysis, like that in the original article that began this thread. But you can never persuade a populace against their will. or at least, not quickly...