"If I understand right, US citizens only owe income tax if what they already paid is less than the US rate."
I'm not an expert, but my understanding is that unless there's a tax treaty specifying otherwise (which we do have with many countries), all personal income over the "foreign earned income exclusion" (roughly 100k) is subject to income tax just like US-derived income would be. (Edit: just saw your edit about Form 1116... thanks, I didn't know about this. But I guess my point still applies in that, tax credit aside, you are still considered to be under the authority of the IRS even if your life and all your income are elsewhere.)
"If something similar were applied to the tax on corporate profits, then it would not change much, as the US rate (21% I think) is pretty low by world standards. But there are exceptions, like Ireland (6-12%, IIRC)."
Right, but if we taxed all international profits, it could probably be very low (maybe "But isn't the Irish company a different entity anyway? How far down the chain of ownership / authorized-importer-relationship would such a rule go?"
My thinking is that perhaps we should end this silly game of international subsidiaries being treated like separate entities for tax purposes and just tax the aggregated profits of the parent entity, regardless of where in the world or under what subsidiary they are realized.