It's hard to judge people from an historical perspective; different times, different morals. Sure, he wanted to convert the heathens but look who he worked for. Also, there's this image of native Americans as pure when they caused the mass extinction of large numbers of native species. Not that they deserved what Europeans did to them, mind you, but they are just another member of the very destructive race of man.
"Columbus was not the first European mariner to sail to the New World?the Vikings set up colonies (c.1000) in Greenland and Newfoundland (see Leif Ericsson and Thorfinn Karlsefni)?but his voyages mark the beginning of continuous European efforts to explore and colonize the Americas. Although historians for centuries disputed his skill as a navigator, it has been proved that with only dead reckoning Columbus was unsurpassed in charting and finding his way about unknown seas. During the 1980s and 90s the long-standing image of Columbus as a hero was tarnished by criticism from Native Americans and revisionist historians. With the 500th anniversary of his first voyage in 1992, interpretations of his motives and impact varied. Although he was always judged to be vain, ambitious, desirous of wealth, and ruthless, traditional historians viewed his voyages as opening the New World to Western civilization and Christianity. For revisionist historians, however, his voyages symbolize the more brutal aspects of European colonization and represent the beginning of the destruction of Native American peoples and culture. One point of agreement among all interpretations is that his voyages were one of the turning points in history."
PS Don't take what people say here seriously, this definitely isn't the place to do such research. A Google search would turn up more useful info.