Having written this, I think it's worth pointing out the main flaw that I see in nationalism: it's that it uses culture and nations as a proxy for principles, as opposed to digging for the actual principles underneath.
As an example, I stand for freedom of speech, in the form of a diverse, largely independent set of publishers and authors that allows me to make up my own mind by exposing me to different viewpoints. Many Western countries have a better track record at this than authoritarian countries. But this doesn't mean that I'm on Team "The West" - if my country drops this value, I'd rather drop my country than my values.
If my country thinks that skin color or wardrobe of a person is more important than what that person is saying, I'd rather drop my country than team up against that person.
If my country decides that Islamic Law or autocratic dictatorship is a better form of government than democracy, I'd rather drop my country than abandon my principles.
It's great to be in a shared space where you agree with everyone. The question is, when you eventually disagree (because you don't get to choose what your neighbors think, and because nationalism is just a proxy for actual values), then are you going to follow your principles, or do you let your nation and culture dictate what your principles should be?
