what is the main thesis of lies my teacher told me?

The main thesis is that U.S. History books, no matter how
well intentioned, have primarily presented only the "good" side of American history.
James Loewen, the author, states that people like Christopher Columbus, and most
American Presidents are presented as heroes to the point that they are almost
mythological; that theirs was a past so glorious that no mere human could have
accomplished all they did; and that we mere mortals have no chance to aspire to such
great heights. In fact, Prof. Loewen goes to great length to demonstrate that the men
and women who created this country were just that, with their own flaws, weaknesses, and
personal demons to overcome. The father of our country, George Washington, was also a
slave holder who sold his slaves if they attempted to escape. Woodrow Wilson, of the
Fourteen Points and Pulitzer Prize winner was an unrepentant racist who removed all
blacks from his administration. And Helen Keller, the poor deaf/blind lady was also a
socialist who kept a red flag over her desk. Yet American textbooks overlook these facts
to create heroes in a process he calls "heroification," not unlike calcification--by
turning them into something they were not.