I agree essentially with you, if perhaps my reasons are more 'Nationalism-is-just-plain-wrong' than 'Nationalism-is-outdated'. You can't speak as if Nationalism did have a hey-day when it was relevant, because it has done little good in it's existence, apart from perhaps win a few football matches. I would also disagree that borders are open. For some countries perhaps, but others not. I'm thinking primarily at this time of the People's (HAHAHAHA) Republic of Korea.

Marching around blowing hot air about how much better your country is only leads to rivalry. And rivalry leads to conflict. (And fear leads to anger, etc. etc. :P)