Says who? According to you anything that Congress says is in the general welfare and can pass into law in the name of the general welfare is constitutional.
Actually, you nor the Congress gets to say what's in the general welfare, the Constitution enumerates what's in the general welfare.
Again, I'll give you the observations and opinions of Jefferson and Madison on the general welfare.
Thomas Jefferson Opinion on Constitutional Interpretation Date: February 15, 1791
“They are not to do anything they please to provide for the general welfare , but only to lay taxes for that purpose. To consider the latter phrase not as describing the purpose of the first, but as giving a distinct and independent power to do any act they please which may be good for the Union, would render all the preceding and subsequent enumerations of power completely useless. It would reduce the whole instrument to a single phrase, that of instituting a Congress with power to do whatever would be for the good of the United States; and as they sole judges of the good or evil, it would be also a power to do whatever evil they please . . . . Certainly no such universal power was meant to be given them. It was intended to lace them up straightly within the enumerated powers and those without which, as means, these powers could not be carried into effect.
"If Congress can employ money indefinitely to the general welfare,
and are the sole and supreme judges of the general welfare,
they may take the care of religion into their own hands;
they may appoint teachers in every State, county and parish
and pay them out of their public treasury;
they may take into their own hands the education of children,
establishing in like manner schools throughout the Union;
they may assume the provision of the poor;
they may undertake the regulation of all roads other than post-roads;
in short, every thing, from the highest object of state legislation
down to the most minute object of police,
would be thrown under the power of Congress.... Were the power
of Congress to be established in the latitude contended for,
it would subvert the very foundations, and transmute the very nature
of the limited Government established by the people of America." (James Madison)