The problem isn't that liberal authors present their opinions or interpretations of history from an obvious left-wing bias. The problem is authors who actually distort facts and manipulate data in an effort to appear objective and unbiased while furthering their leftist objectives.

Students learn, for example, that the Founding Fathers were elitists who drafted the Constitution in order to protect their own economic interests; that Lincoln issued the Emancipation Proclamation only because he needed black soldiers; That racist groups such as the KKK represented our society in the early twentieth century; that the failures of capitalism caused the Great Depression. All false, as readers will discover.