Seems like @Sols has updated his signature, I can't find the thread.
And no, you're wrong. There is no such law. There is plenty of case law from e.g. Germany and the UK where people left to sail on their boat for the rest of their lives and the tax authority agreed that those people are no longer tax residents in their home country.
Yes, you could be taxed based on your citizenship, your hair color, your sexual preference or any other arbitrary criteria. The only requirement would be for this to written into a law, like the US has done. Strangely, none of those claiming otherwise are able to point to any such law. The best thing they can come up with is the OECD template for tax treaties - but tax treaties cannot add new tax liabilities, they can only limit existing ones.
There are indeed cases where the country you leave requires you to take up a new tax residency, e.g. Spain, Australia. But they would require you to actually live there. If you just show them your paper residency from Paraguay without any proof that you've properly established yourself there, they will continue to tax you.
The real reason why being a PT is difficult in practice is that people tend to establish bases somewhere. E.g. in their parents' house, or maybe they create some sort of base somewhere else. It's these bases that can create tax liabilities. Or if they return to their home country after 1-2 years, that home country may also claim you were not really "gone", but just on an extended vacation, and then they might also tax you for the time of your absence.
But if you're truly, properly gone, most countries don't tax you.
You can look at this KPMG flowchart for UK tax residency:
https://assets.kpmg.com/content/dam/kpmg/pdf/2016/01/statutory-residence-test-flowchart.pdf
Nowhere in there is citizenship mentioned as a criterion. Because it is not relevant.
And no, you're wrong. There is no such law. There is plenty of case law from e.g. Germany and the UK where people left to sail on their boat for the rest of their lives and the tax authority agreed that those people are no longer tax residents in their home country.
Yes, you could be taxed based on your citizenship, your hair color, your sexual preference or any other arbitrary criteria. The only requirement would be for this to written into a law, like the US has done. Strangely, none of those claiming otherwise are able to point to any such law. The best thing they can come up with is the OECD template for tax treaties - but tax treaties cannot add new tax liabilities, they can only limit existing ones.
There are indeed cases where the country you leave requires you to take up a new tax residency, e.g. Spain, Australia. But they would require you to actually live there. If you just show them your paper residency from Paraguay without any proof that you've properly established yourself there, they will continue to tax you.
The real reason why being a PT is difficult in practice is that people tend to establish bases somewhere. E.g. in their parents' house, or maybe they create some sort of base somewhere else. It's these bases that can create tax liabilities. Or if they return to their home country after 1-2 years, that home country may also claim you were not really "gone", but just on an extended vacation, and then they might also tax you for the time of your absence.
But if you're truly, properly gone, most countries don't tax you.
You can look at this KPMG flowchart for UK tax residency:
https://assets.kpmg.com/content/dam/kpmg/pdf/2016/01/statutory-residence-test-flowchart.pdf
Nowhere in there is citizenship mentioned as a criterion. Because it is not relevant.