Why is paying for health care such a mess in America? Why is it so hard to fix? Cross-subsidies are the original sin. The government wants to subsidize health care for poor people, chronically sick people, and people who have money but choose to spend less of it on health care than officials find sufficient. These are worthy goals, easily achieved in a completely free-market system by raising taxes and then subsidizing health care or insurance, at market prices, for people the government wishes to help.

But lawmakers do not...