The administration argues that the decision is easy: exchange coverage will be cheaper for most people. Even if that were true, the collapse of the federal healthcare.gov website has thus far prevented all but the most determined from purchasing coverage. That situation is unlikely to be resolved by the promised November 30 deadline.

But for many, exchange plans will not be less expensive. A Kaiser Family Foundation study finds that about half of people now buying their own insurance will be eligible for a tax credit. Perhaps another 20 percent will be eligible for Medicaid coverage. That leaves a third—about 5 million people—paying the full premium.

The Affordable Care Act changes the rules of the individual insurance market. Insurers can no longer reject applicants, and they can no longer charge higher premiums for those likely to incur above-average expenses. Moreover, all policies must now cover a wider array of services than typically available in the individual market.

That raises the cost of health insurance, and the money has to come from somewhere. The federal exchange subsidy only fills part of the hole, and only for some people. The rest is supposed to come from younger, healthier people whose premiums will be higher than their expected cost—and in many cases, substantially higher than they pay today.