>There is, for a number of reasons, but not least of which is fairness. If I get a dollar, then the size of the economy doubles, my purchasing power as a fraction of the total amount of economic activity doubles. This creates wealth inequality over time.

You assume that as an economy doubles prices won't decrease. The natural tendency of a free market is a decrease in prices due to competition, technological innovation, and other factors. If anything, holding the same dollar will lead you to purchase more goods at a higher quality than before as the market develops and expands - a higher purchasing power.

Wealth inequality is exactly what is caused when you print money to match the growth of the economy due to the aforementioned Cantillon effects.

>Most importantly, philosophically, nobody owes you a risk-free return over time on your idle, un-invested capital.

There is nobody that is giving you that return. The so-called "return" is the tendency of a free market to lead to cheaper prices and higher quality goods and services. If anything, I can't see a justification to allow the public's money to decrease in value over time.

>You mean the industrial revolution? I'd say there were externalities that affected that. Counter-point, the great depression.

Yes, there were externalities that affected it, but the core point remains the same. Competition and rapid technological innovation lead to a decrease in prices over time. The Great Depression was not a consequence of a natural deflationary regime rather it was the consequence of extremely lose monetary policy during the 1920s ("The Roaring Twenties") and it would have resolved itself quite quickly but as letting people be unemployed is usually politically unpopular Roosevelt enacted price controls that extended the market correction process that would have otherwise taken a much shorter time than it did.