This is why arguments about this go in circles. You either argue from a pure theoretic POV back and forth, or you go off data - at which point, bringing up every failure of free markets (like, obviously, US healthcare) is dismissed as "not really a free market"
Even the theoreticians on the free-market side are far less solid than.. all the other sides (behavioural economics, information asymmetry.. even Marx) but I regard it as deeply unpragmatic when there's so much data out there indicating what actually happens in the real world when you go one way or the other.