"With respect to the two words "general welfare," I have always regarded them as qualified by the detail of powers connected with them. To take them in a literal and unlimited sense would be a metamorphosis of the Constitution into a character which there is a host of proofs was not contemplated by its creators."
Constitutional architect James Madison in a letter to James Robertson
"If Congress can do whatever in their discretion can be done by money, and will promote the General Welfare, the Government is no longer a limited one, possessing enumerated powers, but an indefinite one, subject to particular exceptions."
James Madison, 1792
I'll take their word for it!
Promoting the general welfare was a PURPOSE behind those powers granted - it was not itself a power granted.
Regulation of commerce between the States is a power granted to Congress. But if it is the power to regulate ALL commerce - and any activity that might effect commerce - and even non-activity that might effect commerce - then our founders did not bequeath to posterity a government of limited and enumerated powers - but one of limitless and innumerable powers.