Stuart Taylor, a judicious analyst of legal matters, says (in the National Journal) that the Supreme Court probably would uphold the constitutionality of the mandate, for two reasons: Because uninsured people create substantial economic effects by seeking free care from emergency rooms. And because the mandate is, in Congress’s judgment, “necessary and proper” for financing health-care reform.
But if any activity, or inactivity, can be declared to have economic consequences, then anything can be regulated — or required. Furthermore, judicial review — and the Constitution itself — is largely nullified by a doctrine of virtually unlimited judicial deference to Congress’s estimates of what is “necessary and proper” for the regulation of commerce.
If Congress does something beyond its constitutional powers, that something does not become constitutional merely by Congress saying it is necessary for this or that.