[jerf]

Basic differential equations: Any system with an effect proportional to the negative second derivative in it will tend to have cyclic behavior. That's a bit oversimplified, but in practice it often works out that way. And there's plenty of such things in the economy, so cycles in the economy are inevitable.

You can make solid cases that we don't need to have quite the crashes we actually do. But I don't believe in the existence of a real economy that doesn't have some substantial cycles in it that people will point to as evidence that something is wrong.

(Of course, if enough of those people get together and get put in charge of an economy, they often are successful at removing the cycles, by virtue of removing all instances of the economy going up at all....)