A functioning market is one where multiple market participants exist (both buyers and sellers) and both are able to make educated choices.
How can a market like this exist when the buyer is incapacitated, not to mention even when not incapacitated, the buyer is not sufficiently educated to understand what they are buying?
You could buy the services of an expert in medical decision-making who will negotiate for you when you're incapacitated.
Also, supposedly people aren't total dicks. At the moment the healthcare industry rewards a lot of psychos due to its incentives. Hopefully with a free market the dicks would be weeded out due to increased choices. Also having a free market means that there would be an incentive to make medicine more accessible, while still correct, because more people could be willing to become healers, maybe specialized healers. Who knows, what's certain is that we have not discovered the full potential of humans healing other humans and the current regulations are a big brake on new systems and innovations.
So, for now I'm ok with the whole single-payer/universal healthcare deal.
Or you can just not do free market on something that should be a human right given the capabilities of modern medicine. It shouldn't be left up to market forces to decide who gets help. That kind of makes sense for some things like TVs and laptops but not life and death when for the most expensive items your only choice is life and death.
How can a market like this exist when the buyer is incapacitated, not to mention even when not incapacitated, the buyer is not sufficiently educated to understand what they are buying?