Sections 8 and 10 are there by design. James Monroe was the leading champion (T.J. Norton, p.51), so I shall herein call the Commerce Clause "The Monroe Doctrine" --one that did and does more for the greatness of the U.S.A. than the better-known doctrine of the same name (actually the work of J.Q. Adams, anyway). One could equally well name it the "Turgot Doctrine" after a great French economist and statesman of the 18th Century who devoted his life and career to removing France's interprovincial trade barriers. Turgot never set foot in America, but was one of our true "Founding Fathers" because of his direct influence on several leading Americans who learned from him when they represented the colonies in France. This is a story in itself (Appendix I).
Media and academic pundits slight domestic trade, yet this is the basis of our greatness. They write and speak of "trade" and "commerce" and "specialization" as basic good things, but synonymous with international trade. (Look up "commerce" in The New Palgrave Dictionary of Economics: it says "see International Trade.") States and cities speak of their export industries as their "economic base," yet their internal trade is far more important (Jane Jacobs, among others, has nicely demolished this hoary "economic base" fallacy). Consider the case of The Erie Canal: it thrived and made money for 20 years, 1825-45, based purely on internal trade, inside the State of NY (Carter Goodrich, Philip Cornick).
Neo-con "free traders" push free international trade, while also pushing AGAINST interstate trade. How much sense does that make? Worse, it is not clear that California would or could make e-retailers in foreign NATIONS collect and remit sales taxes on California buyers. There is this delicate question of national sovereignty, as Senator Jesse Helms discovered when Canada defied his "Trading with the Enemy" Act and pointed out that American-owned firms exporting from Canada could sell to Cuba if they darned pleased -- which they did. Thus, if California wins against Amazon, but cannot block or tax sales from Mumbai, we will end up with a negative protective tariff. This is either a major unintended consequence, or, with a touch of reasonable paranoia, a silently intended one calculated to benefit giant firms that have outsourced.
4. How Congress might circumvent the Monroe Doctrine - but probably won't.
A. "The consent of Congress."
States may tax imports "with the consent of Congress." McGoldrick v. Berwind White (1940) also established they might apply a sales tax if the seller has a "nexus" (physical presence) in the taxing state. Quill Co. v. N.D. 1992, seems to have established that Congress (not any state) has the power to enact legislation letting states levy sales- and use-tax on remote sales, including mail-order and electronic sales, without the current requirement of physical presence. Congress and the President have the power to require all online vendors (and all mail-order sellers) to collect sales- and use-tax on all sales to all states.
That's interesting, but only speculative and hypothetical to date because Congress doesn't pass laws just because it may. It also has power, for example, to tax capital gains as they accrue, but it never has, and the leading case where the U.S.S.C. ruled that Congress has this power under the 16th Amendment is usually cited, tendentiously and misleadingly, to show the opposite. This is because the Court told the Wilson Administration it needed the consent of Congress (Eisner v. Macomber, 1920); it is Congress that has the power to define taxable income, which the 16th Amendment does not. Congress has never given this consent, but it could, any day of the week.
For another example, the very first power the Constitution enumerates for Congress is the power to levy a national land tax (Art. I, Sect. 2, Para. 3), but it hasn't since 1862.
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