I read a bit about the World Service Authority after reading their definition of world citizen in the conveniently named World Citizenship Defined article. While I really enjoyed the article itself, it’s coming from a very idealistic place that I don’t completely agree with (there is no particularly rational argument to back up my disagreement – I acknowledge it stems from a very idealistic perspective that wishes cultures could be preserved as much as possible in the face of globalization). The WSA presents globalization, or a universal global identity as their article implies, as the solution to the world’s problems. This global identity is one that would do more to unite humanity than nationality or whatever else divides it. All divisive identities, like pesky nationalist sentiments, would then have to be unlearned.
Citizenship was defined as “restrictive rights and duties within a given social structure,” which would make world citizens restricted to the rights and duties to a global social structure. In terms of popular sovereignty, everyone in the world would get directly be involved in making decisions for the world, ideally. This undermines the idea of nations and nation-states. Beyond being open-borders, the World Service Authority seems to be against the idea of any borders at all -being an immigrant from an underprivileged background, I would absolutely love this, but I doubt it’s a very popular idea among people with any power. 
Besides this, the WSA created world citizen passports, which are mostly useless, but they serve some kind of symbolic point, I think. They also handed these out to stateless people and refugees -again, these passports are invalid in most countries.
I thought these ideas were super cool, though, again, super idealist, but it did raise one big question for me that has been on my mind for a while: is it possible to impose democracy? If we are all to be global citizens that are affected by and affect a global system with everything we do, must all global citizens fall under the same government system, if a government system is to have a place in a truly globalized world. If so, democracy seems to be where this article is leaning. To those places that do not have democracies, should it be imposed? Will the global minorities and underprivileged people be governed by the majority or hegemonic west (would there be a hegemonic west in the hypothetical global citizens’ world?)?
One statement I did find very interesting was the claim that national sovereignty was “a hangover from the feudalism…” It reminds me of the idea of global feudalism by immigration ethicist Joseph Carens. In very basic terms, he states that the world is organized in a way that resembles feudal societies. There are those nations at the top, those under them, those under those, and so on…and that mobility from a lower state to a higher state is near impossible. Career prospects, education opportunities, and even recognition are strongly influenced by where one is born on a national level.