States [of the USA] selectively comply with federal law all the time - an obvious example is Colorado legalising marijuana.
You seem to think it's reasonable that there is some oversight body for federal law, so why not an oversight body for international law? Why would you consider it 'good' that there's no consequence for Brazil, up to the point of all-out war?
states can play this game in limited circumstances where the federal government makes only a half-hearted effort at enforcement. if the national opinion were more united against recreational marijuana, there are plenty of ways the federal government could force colorado to comply (eg, withholding highway funds).
Because such a body would require a world government, no such government exists, and its existence would be a bad thing.
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; but all Duties, Imposts and Excises shall be uniform throughout the United States;
To borrow Money on the credit of the United States;
To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes; ...
I read right over the words you wrote because I'm so used to the phrase interstate commerce and not at all used to seeing intrastate commerce. I wasn't trying to use Article I to argue that the federal government had any right to regulate INTRAstate commerce. Sorry about the mixup.
So, now your original point makes much more sense, and I completely agree with you. Thanks for taking the time to reply.
(The federal government can't force all states to do something because 1. the federal government's force is limited by its powers, and 2. the states together have powers to overrule the federal government)