I used to try and combat the amazing ignorance of international-law-hating self-styled libertarians too, but eventually I decided it was bad for my blood pressure. And Mr Gray does it far better than I.
Incidentally, I’d be delighted to see a World Government. Not because I think it’d be any better than anything we’ve got now (although there’s no particular reason, based on the examples of the EU and the UN, to believe that it would be appreciably worse), but because it would really, really, really annoy most of the people I despise.