The relationship of many American leftists to patriotism reminds me a lot of those guys who grow up in oppressively evangelical communities and decide to express their disillusionment with it by becoming black metal satanists - a oppositional mirror of Christianity - instead of becoming atheists.
Like the correct response to the realization that nationalism is a false consciousness used to suppress class conflict is to focus on raising class consciousness not to root against the nation everyone around you is rooting for.