Consider:
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...
Then consider the social unrest caused by high unemployment and poverty during the depression.
Rather, they would have used a word like "charity", or "for charitable contributions", or "for the poor". The term "general welfare" already applies to things that the feds were already empowered to do.
Also consider, that if we take a loose flexible interpretation of "general welfare", and if we consider that later Amendments over rule earlier ones where they are in conflict, then congress could claim it empowers them to do just about anything, as long as they feel it is for the "general welfare".
For instance, they could pass a law against the Christian bible because it upsets gay people. For the general welfare you understand. The first amendment swept aside, because it is conflict with "general welfare"...