Outside the US the Left is fanatically nationalist and patriotic. In fact, at one time during the Cold War Communist propaganda referred to the Communist side in any conflict as the "patriotic" side. And can you imagine any classroom in North Korea brainwashing their citizens into believing that their "lousy" country shouldn't even exist in the first place?
Communism seems to make other countries militarily strong and assertive (USSR, China, Cuba, etc.). No one messed with any of those countries under Communism. I honestly believe a Communist USA would be such a self-hating entity, it would intentionally attempt to destroy itself.
The Western Left outside the USA is pacifistic, but still nationalist and patriotic (eg Scottish National Party). A Communist USA would be not only unarmed, but self-hating.
Not to get anyone mad at me, but though the American Revolution was not a social revolution, it gave inspiration to other revolutions that were--such as the French Revolution. One could make the point that without the American Revolution (or a failed American Revolution) the Left as we know it today would never have come into existence in the first place. This makes the Left's monomaniacal and almost genetic hatred of America especially irrational.
The societal change brought on by our revolution was as radical and revolutionary as any in history.
In destroying monarchy and establishing republics, our founders knew they were changing society as well as government.