Yglesias goes on from here and says this:
One interesting issue here regards preventive care. Things like regular checkups, wellness advise, basic screening, etc. don’t meet the definition of “genuinely insurable risks.” At the same time, based on what we actually know about medicine an ounce of prevention really is worth a pound of cure and as long as you’re going to be having the state pick up the tab for illness it seems very practically sound to also have the state invest in prevention. But defining what does and does not count as “prevention” would entail a degree of non-Hayekian planning. My take would be that these medical issues are sufficiently technical to think that Hayek’s general point about the superiority of the market to technocracy in organizing knowledge almost certainly doesn’t hold.[E.A.]I'm not convinced by this argument at all. While it's no doubt true that the science of medicine has grown quite complex and technical, so has our society's ability to receive, analyze, and share information. This ability puts us in a good position to determine what constitutes effective care.
I think that this would be especially true in the case of preventive care, which is likely to tend toward the basic end of the treatment spectrum. In the case of more advanced treatments, it should still be the case that the non-expert can educate himself about the effectiveness of various treatment options, even if the underlying biological or chemical mechanisms of the treatment are not well understood.