ACA require everyone to buy health insurance. Otherwise something called adverse selection kicks in - only those likely to get sick buy insurance making it prohibitively expensive for those who remain. Justice Scalia doesn't get it:
You could say that about buying a car. If -- if people don't buy cars, the price that those who do buy cars pay will have to be higher. So you could say in order to bring the price down, you are hurting these other people by not buying a car. (See here page 19 line 10)Anyone who has opened an economics text book can answer that one. If some people don't buy cars then the demand for cars falls. The price falls not rises. (The demand schedule moves down and intersects the supply schedule at a lower point giving a lower equilibrium price.)
You might want to argue about whether supply curves really slope upward the way they do in textbooks but that is beside the point. The issue is that insurance is not like a textbook competitive market and the comparison with cars or broccoli is irrelevant. Adverse selection is a market failure and governments need to intervene to correct it.