I'm not sure either of the above answers truly answers the question presented, although the question itself is perhaps overstated.
Columbus's image as a hero comes from the works of two people: Washington Irving, of Rip Van Winkle fame, who served as U.S. ambassador to Spain and wrote a four volume biography of Columbus. Irving is the author of the legend that Columbus proved the world was round; that no one believed him and of his friendly treatment of the natives. Also, Samuel Eliot Morrison, a historian and naval scholar who retraced Columbus's steps and concluded that most of his discoveries were by dumb luck.
Historians took no great interest in Columbus until 1992, the quincentenial of his landing. At that time, the Catholic Church considered canonizing him. It was the combination of the date, the Church's attitude and protests from Native American peoples that led to further investigation into his actions and a revision of the Columbus myth.
The above post states Columbus was not responsible for the disease that killed millions of Native Americans. True; however he was responsible for kidnapping and enslaving a large number of Native Americans, forcing them to search for gold and cutting off the hands of those who did not meet their quota; and also turning attack dogs on the Natives when he made his first return voyage. The dogs literally tore the flesh from the limbs of the Indians while Columbus watched. All school children for years have been taught that Columbus carried Indians back to Europe; only recently have they been told that the Indians were kidnapped when they were tricked into boarding his ship.
Columbus may not have been personally culpable for the genocide of disease and forced labor which decimated Indian populations; however he bears tremendous responsibility for the ill treatment they received either at his hands or at his direction.