[selectionbias]

As someone has already commented, the definition of an 'efficient market' in no way equates willingness to pay with utility, and in fact economists seldom make this assumption. Pareto efficiency is very deliberately not utilitarian. A Pareto efficient outcome needn't be a 'good' outcome, it is just an outcome such that no other outcome would make everyone better off. If an outcome isn't Pareto efficient then there is room for improvement. It's worth noting that while Pareto efficiency is central to some very neat foundational concepts taught in introductory econ, modern ecenomic research uses a range of welfare measures to quantitatively evaluate policies. This includes utilitarian welfare analysis. These maybe better capture the actual ethical goals we should have when making policy decisions, but they are usually a bit ad hoc and don't lead to such neat results.