Madison on the Commerce Clause

According to James Madison,

It is very certain that [the Commerce Clause] grew out of the abuse of the power by the importing States in taxing the non-importing, and was intended as a negative and preventive provision against injustice among the States themselves, rather than as a power to be used for the positive purposes of the General Government.

Letter to Cabell, February 13, 1829.

I'm assuming he would know the motive for including the clause, and how it should be interpreted.

Yet, in Wickard v Filburn, the Supreme Court decided otherwise when they declared a farmer growing wheat for his personal consumption had to comply with FDR's arbitrary dictates. For the horrid details, see the book The Dirty Dozen by Levy and Mellor.