The reason that history matters is demonstrated within the body of your question. Without knowledge, humans do all kinds of things that are bad for them: if they know nothing of nutrition and exercise, they sacrifice their health; if they don't know that fire is hot, they burn themselves; and if they think that the British or Germans fought in the civil war, that effects our relationship with the Germans and the British.
Beyond that, we owe a duty to the truth - when human beings "know" things that are untrue, bad things happen. Case in point: someone wrote an article about Q'uaran burning in Gitmo, Muslims rioted, people died. But by the time it was known that the story was untrue, the apologies fell on deaf (actually dead) ears.
Your question also demonstrated another concept: when people are not given all the details, they simply fill in the gaps from their own imagination.
(As an aside: Palin was actually right about Paul Revere's ride, although she did mangle it quite a bit - the purpose that the British were going to Concord was to disarm the rebels, and Revere was in fact captured by the British and warned them that the rebels were prepared for them)