What Should we have learned from the Vietnam War??

Since I served as Civil Affairs Officer there, and later as Advisory Team Leader north of Kontum, and then in the so-called "Iron Triangle", I am uniquely qualified to answer that vital question, lest my fellow Americans follow in my footsteps and repeat my mistakes:
Was the US trying to bring freedom and democracy to South Vietnam? NO! The US prevented the nationwide election scheduled for 1956 and the 1954 Geneva Conference. According to then President Eisenhower: "I have never talked or corresponded with a person knowledgeable in Indo- Chinese affairs who did not agree that had elections been held at the time of the fighting, possibly 80 percent of the population would have voted for the communist Ho Chi Minh as their leader.
By 1965 nothing had changed, according to US "pacification" chief John Paul Vann:
A popular base for the government of South Vietnam does not now exist - The existing government is oriented towards the exploitation of the rural and lower class urban populations - the dissatisfaction of the agrarian population is expressed largely through alliance with the National Liberation Front, which the American politicians and the press call the 'Viet Cong'.