The point of my comment was that, in the US, the government has to create an elaborate body of law to trick people into thinking the law says something which it does not say. If we did not have limitations on the taxing power of congress, they could just write a simple law that says "There is hereby imposed on all labor of every person working in the 50 states a tax equal to..."

The fact that there is no such sentence in US tax law should be a wake-up call... The reason the income tax parts of the IRC are so complex is to keep them in perfect accordance with the constitutional limits on taxation while deceiving you. Taxes on income are in their nature excises, which are taxes on privileges. Foreign persons do not have the same rights that we Americans do (I don't necessarily agree with this, it is just how the law works).

Eventually this will come to an end. Tens or hundreds of thousands of people have known about what I am saying for a hundred years. Eventually a critical mass of people will be wise to the scam and HR departments will no longer subordinate perjury by pressuring clueless people to improperly sign a Form W-4, declaring themselves to be a foreign person subject to wage withholding (see Treasury Decision 8734)[0].

[0] https://www.irs.gov/pub/irs-irbs/irb97-44.pdf