In reading the writings of James Madison, it appears that people have been debating this very issue of what does "Provide... for the general welfare of the United States" mean and not mean.
Both Thomas Jefferson and James Madison were of the mindset that this clause did not grant congress unlimited powers.
So this is not a new debate nor one that is easily solved I am afraid.
Our Constitution, like other Constitutions, was a compromise and has different interpretations. Hence the need for a Supreme Court.
So far, the Supreme Court seems to be supportive of what Congress has been doing for at least the past 100 years.