Block points out that people are subject to pessimistic bias against markets, that because people are without X now, they will continue to be without it in the future. We have the humanitarian high ground because nothing has ever brought humanity out of the dumps like capitalism. You can win via empiricisim.
Alternatively you can use theory. The way human beings get more stuff is through balancing capital investment, savings, and consumption. Only a free price system can transmit information effectively. Life is not “sim city” where you can simply demand that more healthcare be produced for 100 simoleans.