Guys,
perhaps a discussion of U.S. v. Butler, 297 U.S. 1 (1936) will help add some understanding to this debate. It illustrates where the US was, and where it remains today on this issue.
Prior to 1937, there was a debate as to whether or not Congress could spend for whatever purpose it wished (so long as the "general welfare" was being served), or whether Congress could only spend in order to carry out one of the other enumerated powers listed in Article I, Sec. 8.
In U.S. v. Butler, the Court held that no such limitation exists -- the spending (and taxing) powers are themselves enumerated powers, so Congress may spend (and tax) to achieve the general welfare, even though no other enumerated power is being furthered.
The Court first concluded that the power to "tax and spend for general welfare" existed as a power separate and distinct from the other powers enumerated in Article I, Sec. 8. Thus the taxing-and-spending power stood on equal footing with, say, the power to regulate interstate commerce.
But, the Court rejected the contention that Congress has an independent power to "provide for the general welfare" apart from the power to tax and spend. Thus Congress may not regulate in a particular area merely on the ground that it is thereby providing for the general welfare; it is only taxing and spending which may be done "for the general welfare." Otherwise, the Court noted, the federal government would be one of "general and unlimited powers," rather than enumerated and limited ones.
The most important principle for which U.S. v. Butler stands today is that Congress has NO POWER TO REGULATE for the purpose of providing for the "general welfare." Congress MAY spend for the general welfare, it MAY tax for the general welfare, but it MAY NOT regulate for the general welfare.
Does this help clear some issues up?