I don't think 7.5% of voters constitutes the average American. Even so, those ignorant enough to believe that the Vietnam war was immoral, stupid, and wasteful, believe it because of lies told by Kerry and others. Those who know the truth are not so easily fooled.
Given the size of the protest movement at the end of the war and the general opposition of most of the population, I don't think that it's a case of the many being led by the few.
Also, look at pop culture: "Forrest Gump", "Platoon", "We Were Soldiers", "First Blood(Rambo)", The Things They Carried etc. The prevailing attitude is that the war was hell for all involved and we would have been better off if we'd never have gone.