The real problem is that the reductio ad absurdum of "free market" is feudalism and that if you look at it, the Magna Carta absolutely limits the rights of free enterprise. John Lewis Gaddis makes a great point in "The Cold War: A New History" that both the US and the USSR ground their economies to nibs championing one form of extreme government of the other while the rest of the world settled on some form of happy medium... and that since there are so many points on the spectrum between capitalism and communism, it's safe to assume that not all systems work the same for all societies.
And to add to your point about free markets leading to feudalism: This has been a known phenomenon since the dawn of modern capitalism. Yet, somehow, libertarians and free market worshipers pretend that Ricardo and Malthus didn't exist (or they willfully ignore everything they wrote), and that the free market experiment has never been tried in earnest. Ask a five year old chimney sweep how well the pure free market works.
The Magna Carta could be looked at in a couple ways. To the nobles that forced the King to sign it, it was guaranteeing freer enterprise, insofar as it made it impossible for him to arbitrarily tax them without consent. But I suppose that's the point of regulation, to ensure that those with less power have a chance against those with lots of power.