[T]he idea that there is a "free market" in health care for consumers is nonsense. A free market assumes that participants are knowledgeable and understand the choices they're being asked to make. That's not the case with health care, as anyone who has tried to analyze Medicare-supplement plans or pick among insurance options offered by his employer can tell you. Should you find yourself in a rural area far from home with a mysterious and troubling pain, you're not exactly in a position to bargain with the local walk-in clinic or hospital emergency room.
If a market is a place of exchange, calling it "free" doesn't tell us very much about its social meaning. Just because two or more parties agree to a transaction doesn't say anything about the balance of bargaining power, or the external pressures that may bring people to that market in the first place.
Anyone in a position of desperation or dependency will engage the world at a disadvantage; for Marx, this was the premise on which modern markets worked: Inequality, the engine of wealth.