You quoted me thus: "And then see the last clause of Section 8 of Article I." And then you proceeded to quote from the first clause of Section 8. I'm talking about the last clause, to wit: "To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof."
The power - indeed, the obligation - to protect the country from invasion is vested in the U.S. government, and any military force is clearly necessary and proper to that end. There is no corresponding grant of power when it comes to "general welfare". The clause you quoted, when quoted in full, is not a grant of power, but a limitation on the power of taxation.
That wouldn't seem to make much sense on a practical or theoretical basis. Clause 18 says "the foregoing powers" which would seem to mean the previous 17 clauses, including the first one. I don't understand how "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;" can be construed as anything but a "power," and therefore covered by Clause 18.