People who think this don't understand the proper order of the sequence of events in a deflationary scenario.

They think that if prices go down, then there's no reason to invest, so the economy stagnates and contracts.

The problem is that price deflation is a CONSEQUENCE of the economy expanding. It manifests only after the economy has grown, not before. And the economy only grows if and when investments produce a positive return.

In effect, their argument is "with a constant supply of money, the economy shrinks if the economy grows"

Doesn't actually make sense.