I disagree that The Omega Glory was a nationalistic message. The Yangs worshiped the forms and the documents of America, but lost the main point that freedom was for all the people. In other words, our rights are not reserved for those who wrap themselves in the flag, but belong to everyone; a point that rather needed to be made in 1968.
One could argue that particular point still needs to be made today...and likely every day so long as bigotry, intolerance, and Republicans still exist.