Appiah defines cosmopolitanism as global citizenship.
The Greek is kosmopolites, which means citizen of the cosmos, of the world; so it is really a way of talking about global citizenship. (Philosophy Bites, 2010, 47-8)
There are two features which characterize cosmopolitanism.
The first is the idea that we are all collectively responsible for one another: the idea that we are a sort of single moral community.
[The second is that] we are all entitled at the same time to live according to different modes of life…they don’t want everybody to become the same, they don’t everybody to become Catholics, or Marxists or even perhaps liberal democrats. (Philosophy Bites, 2010, 48)
These few sentences conclude why I cannot bear nationalism nor strict perfectionism.