Then again, I can't fathom what people would be doing with their money if the stock market weren't there. I imagine they might naturally wind up with some sort of...stock market.
The theory posited above is that you could try to manipulate these signals as a sort of economic warfare. If you expect that every dollar you put into our aforementioned roofing nail factory will get you minuscule or negative return, nobody's going to want to invest in building/expanding nail factories, and they'll put their cash somewhere it can grow instead. This is all well and good so long as you've got happy trading relationships with people who can sell you nails, but if one day the nails stop coming--you've got a supply chain shock until you either open new factories or find someone else willing to sell nails to you. The theory here being that if you had a LOT of goods that became tied up in a single point of failure--someone forcing that failure could create a great deal of internal instability to be exploited for geopolitical ends.