My philosophy professor this past semester, who is a Very Big Name in postcolonialism as well as other areas, hates cosmopolitanism and Appiah quite passionately. His reasoning mainly has to do with the fact that only the very privileged (economically, racially, etc.) can afford to consider themselves "citizens of the world," equally protected and with the same opportunities wherever they go, and blithely assume that everyone else can do the same.

His argument is obviously a lot more complex than that, but it ties into your conversation with your mom, in that cosmopolitanism tends to completely ignore the power of corporate or national hegemony.