Suppose I'm a plumber and you're an electrician. You need your pipes fixed, so you pay me $100. I need my wires fixed, so I pay you $100. At the end we both have the same amount of money we started with, but now your pipes are fixed and my wires are fixed.

You come out ahead as long as the value of the thing you paid for is worth more to you than what you paid for it. And if it isn't then why did you pay that much for it, instead of just not doing it?

This is the regular economy, which is not the topic of this thread. We are talking about wealthy people becoming rich without contributing. Renting has diminushing return for the society. Some things like automatic trading have none.

But that's even better, right? If I pay you $500 for an iPhone, I get an iPhone. If you take that money and spend it, it's "the regular economy" again, and I have to provide whatever you bought. If you don't spend the money then I don't have to give you anything, but I still got an iPhone.

The real problem with this is that then I have to borrow money to buy the iPhone but there is no way for me to ever pay it back, because you never spend the money I borrowed so there is no way for me to end up with it again, meanwhile I'm paying interest on it. So everybody's got a mortgage payment when they should already own their homes.

But this isn't capitalism causing this, it's bad laws. Nobody wants to sell you an iPhone so that Apple will have more money -- they want dividends. Until you tell them that leaving the money inside the company (where it collects interest) results in no taxes but if it's given to the investor to spend or reinvest then the government will be having >40% of it up front. So they take their money as share price appreciation instead. Worse than dividends, but not 40% worse.

That causes capital to accumulate inside corporations, which they then use to buy each other, because what else are they going to do with it? So we get megacorps, which then destroy small businesses and corrupt governments and do evil. Because we tax investing the profits of an existing corporation in a new one, when that's the thing that we need to happen to reduce wealth inequality.

You assume rich people spend all their money. They don't. The accumulate, to buy more renting power to accumulate more. It's getting the economy more and more static.

There are three things a rich person can do with money. They can spend it, they can invest it in a new business, and they can invest it in an existing business.

The third one is the worst for redistributing wealth but it's the one our tax laws give high preference to. That is problematic.

It may be hard to believe but labor productivity has been increasing!

For example (and bear with me, because this is incredibly hard to believe) it is more efficient in terms of amount of food collected per hour to use a farming machine over a field of wheat than it is to chase a guanaco or some other rabbit with a bow.

But so have resources consumption and money concentration.