ObamaCare will be argued next week in the Supreme Court. While the justices will consider the intricacies of constitutional law, at their heart the arguments in favor of the legislation have to do with the economics of health care.

Consider the individual mandate to purchase health insurance. The Obama administration defends the mandate on the ground that a person’s decision to not buy health insurance affects commerce by materially increasing the costs of others’ health insurance. The government adds that health care is unique and therefore can be regulated constitutionally in ways other markets cannot.

In reality, the mandate has almost nothing to do with cost-shifting. The targeted population—the young, healthy and not poor who choose to forgo coverage—has a minimal role in the $43 billion of uncompensated health-care costs. In 2008, for example (the latest figures available), the Department of Health and Human Service’s Medical Expenditure Panel Survey showed that the uncompensated care of the mandate’s targeted population was no more than $12.8 billion—a tiny one-half of 1% of the nation’s $2.4 trillion in overall health-care costs. The insurance mandate cannot reasonably be justified on the ground that it remedies costs imposed on the system by the voluntarily uninsured.