1) Capitalism is creating commodities, like corn, and then shipping them. Picking one billion corn stalks is a lot more cost and effort than picking one corn stalk.
With software nowadays, you create the first product, and then with the push of a button, can duplicate and distribute it to billions, almost instantly, almost for free. What this means is you are not really making a commodity any more. Which means that in those parts of societies where this mode of production prevails, you're not even really working within a system of capitalism any more. The system of production outgrows the economic system it is in, just like town trade and manufacture outgrew feudalism centuries ago.
2/3) The helpful thing is to look at what is actually happening, as in a scientific experiment. The real world is not people sitting on top of piles of money, like a dragon in some fairy tale. Those who get the fruit of other's labor by rentier means - landlords, lenders and most importantly stockholders and owners, can only spend so much on luxury goods. They also need only so much as that aforementioned stacks of Credit Suisse gold bars stored somewhere for a rainy day. Most of the money is reinvested.
Where is the money invested? New construction projects, new companies, new loans - or further capital for existing projects. At companies owned, San Francisco apartments etc., more and more of wages go to profit and rent, as that is necessary for inequality. So the worker has less money to buy commodities. But more and more capital is being spent to build more and more commodities. The workers/consumers can not buy these increasing commodities made by the more enriched investors. Credit can kick the can down the road for a time, but if things don't go back to equilibrium, things get worse (see the 2008 taxpayer TARP bailout of banks, 2000 dot-bomb crash etc.)
There's a documentary called the One Percent, where a conversation between Bill Gates Sr., Warren Buffett and Chuck Collins (Oscar Meyer heir) is retold. He is talking about the inheritance tax (now corporate spinned to be called the death tax) and says if things are as unequal as they are now without an inheritance tax, what will happen when one does happen?
I myself don't think there's some liberal, social democratic solution. Idle class heirs have this self-destructive tendency to pull more and more power to themselves, to the point where they begin to undermine their own long-term power. At some point a very radical change comes. That has been the history of the past centuries. The US depression of the 1930s was so long ago, it's hard for Americans to fathom it, and I would guess most people think it could never happen again, but it could. It could even be worse.