How does patriotism destroy a nation?

Patriotism as defined as love for country is not destructive to a nation. But various groups see patriotism as a bad thing because patriots tend think they are better than people from other nations. It could be argued that these patriots would stand on the border telling insults at each other until war broke out to destroy one of them. However, loving one's nation or having pride in one's heritage also forms the cultural glue that holds them together when they need help from one or the other. So a nation of patriots is always better than a nation of anti-patriots.