All countries have their national myths and tends to distort or distract away from failure.  It is more important to consider the intent behind the myth/distortion than the "lie" itself.  Most national myths/distortions are relatively benign in terms of outcomes.  What we need to watch out for are myths/distortions that lead to resentments, prejudices, racism, or encourage warlike behavior.  In this manner, we can acknowledge that the Washington cherry tree myth is benign, while their unwillingness to recognize the true causes, lessons, and outcome of the Vietnam war, are damaging.