There's another way to get somewhere useful:
Set the maximum amount a person can invest into a company (even via proxy!) at the average cost of a machine. _That way companies have to find many small investors and the people who used to work will just own the robot that replaces them. Effectively you won't have companies that are mostly owned by multitrillionaire investors but all companies will be owned by many small investors. The stock market might just work for that as you will just have to get all companies there and then limit the maximum investments per person. Since this is complicated, you can just ban all the stock market shenanigans where people make money on things that do not really exist or derivatives of things that do not exist or the course changes of nonexisting derivatves of things that never existed. This will free up some capacities for the more complicated actual investments.
And if companies cannot find enough small investors, maybe they're not paying their employees enough to allow them to invest, guess that's the end of their growth, too bad.
Of course big investors can still own small shares in many companies that way but this still does not give them a huge influence in any of these companies and they will be against super corporations as those reduce the amounts of investments the big investors can make since every mega corporation replaces a whole lot of small companies.
Yeah, I get these crazy ideas while sitting around in the university...
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