I posted the following to
"Free marketers" too often ignore two important points of a true free market: buyers have all the information they need and there are no externalities.
If a product has any contamination from peanuts, then any buyer who is allergic to peanuts should have that information.
No externalities means that all costs are paid for in the transaction. If a manufacturer is putting anything in the air or water that could harm someone, that is an externality.