The notion of global citizen is misguided in the first place, because there is no global entity to be a citizen of, at any socio economic level that matters.

Sure you can say that you're a creature of Mother Earth, we're all brothers and sisters united by a common bond, all that; at the end of the day you're still paying taxes to a very specific, non "global citizen" government, and depending on that government for basic services like healthcare or educating your kids.