In a free market, monopoly, and even oligopoly are nearly impossible
Well, I 100% disagree, and I think to the contrary, that it can be logically demonstrated that in a purely free market - monopoly or oligopoly are nearly impossible to avoid in the long run.
The barriers to entry into markets DO NOT only come from government - they also come from capital costs and economies of scale.
Maybe, if there were no government prohibition, you could start a bank in your house. Still, it would be very small, unknown, and therefore very risky for depositors; you would probably have to get an insurance policy for your deposits from a large and trusted company. You, a tiny bank, would probably have to pay a high “retail” rate for your policy. A mega-bank, on the other hand, could buy the same policy at a lower, “whole-sale” rate. The same would be true of everything else you do - renting office space, buying ink for the printers etc. You would be paying a higher rate of overhead for almost everything you do, compared to the larger bank . Furthermore, you might be able to afford 1 or two ATMs, while your mega-bank competitor has dozens - you can advertise with flyers in laundromats, while they can buy catchy ads during the Superbowl. You might be able to compete with the megabank, if you are a genius and have a genius business plan - but, the odds are against you being able to pay a higher rate of interest to depositors while also being able to pay a higher rate of overhead for expenses.
In other words, size leads to efficiency and confers advantage in most industries in a capitalist economy.
It’s true that you can grow corn and sell it in your back yard - but it’s also irrelevant if the large farm next door can do it profitably for half of the price you can. You simply can’t sell corn for $2 if corn of the same quality can be purchased for $1 nearby - and, you probably won’t be able to produce corn profitably for $1 until you get nearly as big as your farming competitor.
This is a very real barrier to entry into markets which exists totally outside of government - it’s part of the logic and practice of free markets themselves.
The problem is, markets stop being efficient if they get too concentrated - both on the top and on the bottom. At the top, too few companies will not compete efficiently - in part because they can turn to rent-seeking (or even outright taxes) instead of competition. At the bottom, people with good ideas can’t try them out in the market, simply because the barriers to entry or risks are too high.
So, the main points are that economies of scale exist, that their existence encourages consolidation, and that continued consolidation ends in oligopoly: unless anyone can challenge these points, I don’t think we can avoid the conclusion that totally free markets, left to themselves, crash into the wall of wealth concentration/oligopoly.
The ‘intelligent steering’ a free-market requires is the creation barriers to economic players becoming either ‘too big’, at the top, or ‘too small,’ at the bottom.
A good example of the latter is allowing individuals to go bankrupt, without putting them in debtors prisons (as lenders would surely prefer). This (non-market) protection makes the economy more efficient, by putting a floor under it which allows people to ‘get back into the game,’ even if they lost a round- if everyone who ever went bankrupt were put in a debtors prisons, many great companies and products wouldn’t exist today - also, who would be brave enough to start a business?
Economic players must also be prevented from becoming too big at the top.
Obviously, this is an economic issue - monopolies are non-competitive and non-efficient. But even prior to that, it’s political - if any entities get too big or too powerful, they will start acting like governments (or take over existing governments), simply because so much wealth and clout in their hands gives them the ability to.