I probably share with ATR a desire for simplifying the tax code, though I bet we depart mightily on how it should be simplified and who would ultimately benefit in the end. As for this example of world income, no one should be getting worked up over this, though I'll bet ATR will do their best. Olympians get subsidized substantially for their endeavor; for those few that are medalists they get a little icing on their subsidized cake, while the other Olympians just get the cake. Sorry, I'm not getting worked up about that. On the other hand this amount of "world income" would seem to be a trivial pursuit of government. Why bother for the sake of medalists only, unless they were doing so out of some type of consistency?
This consistency of taxing "world income" should be viewed in light of the fact that for forty years the financial sector has grown at 2 1/2 times the rate of GDP. We are somehow finding ways to generate capital without the bother of production backing that capital. There are two main ways to achieve that. One is for the Federal Reserve to print money at a greater rate than the expansion of GDP, which they do. Yet this is not even the main way we've "counterfeited capital" (though some think tanks want you to think so). "World income" such as currency exchanges and tricks related to "comparative advantages" provide a way we can get capital without our country producing, though Olympians producing the "service" of their sport differs from this. This also explains why we might be more inclined to tax "world income" than other countries because it's become more important in our economy for generating capital in lieu of production.
I should add that numbers I come up with are from primary research of Census or National Income and Products Accounts data. Dogmatic think tanks, conservative or liberal, are the last place I would turn to for information.