I disagree - look at the so-called Gilded Age in America. That was the height of unfettered, unregulated capitalism and it was certainly free market capitalism. Not only was it a period of huge economic opportunity and wealth for some, it was a period of grinding poverty, abuse, and desperation for many, which made socialism and communism and easy sell.
Probably so. BUT it really wasn't a free market when the monopolies formed and had almost total control of the marketplace.
New technologies in transportation, communication, manufacturing, inventions, etc. caused the market to explode. Some took advantage of it and in a ruthless fashion.
Unregulated capitalism is basically anarchy. Mad Max comes in, kills you and takes your shit. The problem was government was too slow and too corrupt to do much about it. Corruption was widespread in those days and they were not on the ball, too many looking out for numero uno.
The pendulum has swung too far now though and government is over regulating the marketplace and again, the Golden Rule applies, them that has the gold makes the rules.
The problem isn't capitalism, it's the people at the helm. And history proves that governments will run an economy aground if given the opportunity.