There's an old joke about economists that I've always liked. A junior professor goes to his senior colleague with a brilliant new idea. The older man dismisses it. "That may be fine in practice," he sniffs, "but it will never work in theory."
Economists are like that, at least many of them. They don't like to have reality intrude on their abstractions. One of the best examples has to do with mobility. Years ago, I read an article by a prominent economist downplaying the problem of a small-town factory that spews out pollution. What's the big deal, he asked. There must be another town nearby without a soot-belching factory. The residents of the first town could just move over there. Pretty soon the polluter would get the idea.