“We are all human beings, and our nationality is simply an accident of birth.” This is my position on the Olympics and basically all national pride. It has nothing to do with anything, there is nothing to be proud of. No one cares when I think it, it's nice to see others say it.
Culture is the largest difference between people. We are the animal that can (re)program itself. Nationality correlates to culture greatly. So there is still plenty of difference between peoples of the world. Its silly to ignore this.
Culture in itself is an important difference that makes people a lot more interesting to each other. But the examples given are not the same kind of difference: Olympic swimmers aren't expressing their culture. They're all, by rule, doing exactly the same thing. That the one from your nation does it the best says nothing about your culture, and there's no rational reason that swimmer or you should feel some sort of pride about that.