> You are asserting that a free market is unstable and will inevitably lead to a monopoly.
No, I am not asserting that.
I think the first thing to clear up is our definitions. My main point would be that a market that is controlled by a monopoly is not a free market. I would define a free market not as a market that is free from government interference, but a market in which all of the actors are free to participate on a fair competitive playing field.
I think that lassaiz-faire, with the meaning of "hands off" may be a more precise way to describe what you are saying when you say "free market".
I think that a fair competitive landscape is ultimately what we want out of markets. I agree that it is bad when government actions interfere with a fair competitive landscape. But it is not inevitable that all goverment actions will do that, and in many cases government action can help rather than hurt. And similarly, plenty of actions by non-government actors can interfere with a fair competitive landscape as well.
> a market that is controlled by a monopoly is not a free market.
In other words, the thing you are talking about _does not exist_ except in libertarian fantasies. Without a government (the monopoly on force in a region, that controls the markets within) providing the backbone for this - i.e. with features such as courts, police, mint - there is no freedom, because an aggrieved party has no recourse other than violence.