Final answer:
An argument in favor of national health insurance is that it would provide all Americans access to healthcare, addressing market failures and reducing the number of uninsured citizens.
Step-by-step explanation:
One argument in favor of enacting national health insurance in the United States is that all Americans would have access to health care. The existence of government programs like Medicare for seniors and Medicaid for low-income families reflects a recognition that the free market alone may not provide affordable insurance for certain groups. National health insurance could address issues related to moral hazard and adverse selection, which are often present in private insurance markets. Additionally, a national program could reduce the number of uninsured or underinsured citizens, including the millions who were without insurance prior to the Affordable Care Act or 'Obama Care,' despite the criticism it faced for the insurance mandate.