Question

Why is "promote the general welfare" the principle that applies to the debate about universal health care?

Answer 1

The government of the United States is supposed to be a government of limited powers; when the federal government was formed by agreement of the 13 original states, the states gave up their right to govern themselves only to the extent they expressly gave power to the national government under the Constitution. 
The U.S. Constitution does not anywhere expressly grant the federal government the power to provide universal health care (which requires taxing some people more than others and other people receiving more benefits as individuals than others) Those who oppose universal health care say that a law providing universal health care would be unconstitutional. Those who favor this type of law argue that Congress has the power to provide for the general welfare of the United States and that universal health care is part of the general welfare. This same argument was used in support of the Social Security Act in the 1930s and the Supreme Court then agreed that the general welfare was served by old age pensions. 

Article I, Section 8 of the Constitution sets forth the powers of Congress. It begins: "The Congress shall have Power To lay and Collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States". If not for this clause, the federal government would not have the right under the Constitution to provide universal, or even subsidized, health care.

(It should be noted that that is not the Constitution's only reference to the "general welfare"; the crucial importance of this concept is indicated by the fact that the brief Preamble of the Constitution includes providing for the general welfare as one of the reasons that the new nation, the United States of America, was formed.)

What exactly does "general welfare" mean? Is it a separate power of Congress to tax and spend for the general welfare, or is Congress' power to tax and spend limited to those areas which are specifically listed as those in which it make laws and regulate? This is one of those vague phrases in the Constitution that the founders left for future generations to interpret, knowing they could not resolve every possible issue within the few months in which they hoped to create a new form of government. The meaning of "general welfare" because the subject of debate very quickly and is still under debate 225 years later. 

Federalists who believed in a strong central government, such as Alexander Hamilton, argued that the general welfare clause granted Congress a broad power to levy taxes and spend money for the general welfare of the country as well as for purposes specifically listed as powers of Congress. James Madison, one of the principal writers of the Constitution, disagreed, arguing that this made the power of the federal government too broad and that the list of enumerated powers was supposed to limit the purposes for which Congress could tax and spend as well as the purposes for which it could make laws. 
There was limited reason for the Supreme Court to attempt to interpret the general welfare clause until the 1930s, when President Roosevelt and Congress passed a wide variety of new laws in their attempts to bring the country out of the Great Depression. They based their power to do so on the general welfare clause (until then, most broad federal actions were justified by the Constitution's grant to the federal government of power to regulate commerce). The Supreme Court in United States v. Butler (1936) upheld the right of Congress under the general welfare clause to raise money and distribute it in ways not included in the specific list of powers in Article I, Section 8. However, the Court stated that this power was limited to matters affecting the general welfare of the United States as a whole, rather than the welfare of particular areas or people. 
One year later, in Helvering v. Davis (1937), the Supreme Court upheld the old-age insurance provided by the Social Security Act of 1935, stating that although Congress's power to tax and spend under the general welfare clause was limited to general or national good, Congress had the power also to decide what constituted the general welfare. That has been the general interpretation of the law since then. 
Conservatives think the Supreme Court abdicated too much power to Congress, arguing that "general welfare" means the general welfare of the nation as a whole, and that this clause does not justify taxation and spending as a means of redistributing wealth from those who have more to those who have less. That seems to be viewing the country solely as an indivisible political entity, the United States of America. Progressives argue that the country is more than that, it is a collection of over 300 million people, and believe that the general welfare of the people is essential to maintain the general welfare of the nation.