If a currency is deflationary, there's no point to investment - investment is risky, whereas simply holding it gives it more value (this presumes a stable store of value and no alternative currencies).

This tanks economic growth, because beyond a certain quantity of wealth your savings appreciate in value faster then you need to spend them to stay alive. Whereas below a certain value of wealth, no matter how hard you work or how much you save, you will never reach that point - because you have to reduce your savings to buy the necessities of life.

Of course, its not a stable situation because the economy that goes into a deflationary spiral soon collapses, the rich get murdered, and everyone moves back into a currency which supports a proper debt-system and doesn't doom people to servitude for an actual idle rich.