> it assumes everyone has perfect knowledge

Nobody says that. Free markets are actually the best mechanism to deal with situations in which participants have partial/imperfect knowledge.

> I don't need to do a ton of research about what drugs I'm taking

I do, and I recommend all do. Just the other week my ear doctor gave me a prescription for an antibiotic that had as a side effect a significant chance of ligament fracture. I went back and he changed it to a milder, less aggressive medicine.