The "free market" doesn't really exist. It is an ideal, and an ill defined one at best. What does exists are mechanisms. A law that forces prices to be visible

The "free market" doesn't really exist. It is an ideal, and an ill defined one at best. What does exists are mechanisms. A law that forces prices to be visible is a mechanism that is likely to increase economic efficiency at little cost. In absence of a rent-seeking doctor's guild, it would not be needed, true, but it is certainly better than nothing.