It's at this point that I should recall the statement you made that prompted my initial response to you herein: "Do you believe the Founding Fathers would give Congress the power to regulate interstate commerce, yet allow the individual states to undermine and subvert their regulatory efforts?" Since it wasn't their intent to give the federal government power to place actual restrictions on commerce subsisting between states, it would follow that it also wasn't their intent to give the federal government power to restrict that which would allegedly undermine an attempt to restrict commerce subsisting between the states.
The actual exercise of a power may or may not have to conform to the original intent - that's debatable at least. But measures which are "necessary and proper" for carrying into effect a particular power would, among other things, have to be consistent with the reason for which the power was granted.
And from that, I say that it is also fine for Congress to regulate commerce among the several states for the positive purposes of the country (or against the negative purposes to the country).
So if I understand you correctly, you're saying that although it wasn't part of the original intent for Congress to regulate commerce among the several states for the positive purposes of the country, Congress nevertheless has that power. In that case, there was little point to Madison's second letter, beyond raising a matter of mere historical curiosity. I think Madison's reason for bringing it up was more than purely academic. That's the impression I get, anyway.
"As I pointed out, there would have been little reason for him to be concerned about that specifically, since the Constitution already explicitly prohibited that (no taxes on exports from any state)."
Fine. Then change my scenario to Madison fearing that Congress would one day use its regulatory powers to ban cotton from Georgia for the positive purposes of the country.
But there's still nothing in the letter that shows his concerns to be that Congress might unjustly discriminate against one state. Of course it would be unconstitutional if it did, but nothing indicates that that's the limit of his concern. He said that it wasn't the original intent for Congress to be regulating interstate commerce for the positive purposes of the federal government. Now either that statement reflects on the actual legal meaning of the commerce clause, or it doesn't. If it doesn't, then it can safely be dismissed altogether as mere historical reminiscing. If it does, then it means that Congress does not have the power to regulate interstate commerce for the positive purposes of the federal government. It's one or the other.
Stop right there.
IF the individual states erected some barrier to interstate trade, Congress was given the power under the Commerce Clause to remove that barrier. That was the original intent of the Commerce Clause. To "regulate" commerce. I'm sure we both agree on that part.
Now you're making a different argument that "to regulate" does not include "to prohibit". I disagree, provided that Congress prohibits among all the states equally.
Again, I go back to that 1808 case, United States v. The William, 28 Fed. Cas. 614, no. 16,700 D.Mass. which said that the power to regulate commerce is not limited to simply encouraging it:
"Further, the power to regulate commerce is not to be confined to the adoption of measures, exclusively beneficial to commerce itself, or tending to its advancement; but, in our national system, as in all modern sovereignties, it is also to be considered as an instrument for other purposes of general policy and interest."
"The mode of its management is a consideration of great delicacy and importance; but, the national right, or power, under the constitution, to adapt regulations of commerce to other purposes, than the mere advancement of commerce, appears to me unquestionable."
1808.
In U.S. v. DARBY 312 U.S. 100 (1941), the USSC stated:
"The power to regulate commerce is the power 'to prescribe the rule by which commerce is to be governed'. It extends not only to those regulations which aid, foster and protect the commerce, but embraces those which prohibit it...."
Granted, Congress may not have intially used the Commerce Clause to prohibit commerce -- but that doesn't mean that the power wasn't there all along.
Here's an excellent link (yet another robertpaulsen home run) which should put this issue to rest.
"So if I understand you correctly, you're saying that although it wasn't part of the original intent for Congress to regulate commerce among the several states for the positive purposes of the country, Congress nevertheless has that power."
No. I'm saying that Madison's second letter opens the door to using the Commerce Clause in that manner.
If, according to Madison's second letter, it is constitutional for Congress to regulate commerce with foreign nations for the positive purposes of the country, then I'm saying it's constitutional for Congress to regulate commerce among the several states for the positive purposes of the country.
"But there's still nothing in the letter that shows his concerns to be that Congress might unjustly discriminate against one state."
Sure there is. If I say to you that "to regulate commerce with foreign nations" includes the power to place that foreign commerce at a disadvantage for the good of our country, then what are you to conclude if I were to extend that same power "to regulate commerce among the states"?
As Madison says, if taken literally, that power would allow Congress to place one state's commerce at a disadvantage for the good of our country. His second letter says, "Don't do that". His second letter reminds Cavel of the original intent of the Commerce Clause -- to remove barriers to injustice.