I have only one problem with Columbus. He didn't do anything that hadn't been done before.
Discovering the Americas? The Vikings beat him to it by over 400 years. And they even colonized Newfoundland.
Proved that the Earth Was Round? Already been done. At the time, it was widely accepted that the Earth was round. In fact, Eratosthenes, a Greek mathematician of the 3rd and 4th centuries BC calculated the Earth's circumference about as accurately as possible (given the measurements and tools available to him), as compared to Columbus' calculations of circumference which were so off, that he only survived due to the blind luck of there being another continent in between him and Asia.
Conquered, oppressed, and wiped out the natives? Not only was this not exactly new to Columbus' culture, but this definitely wasn't new to the Americas. Conquest and oppression are, unfortunately, endemic to humanity, and occasionally one group or another gets wiped out in the process.
In other words, Columbus didn't do anything deserving of great accolades, nor did he do anything deserving of condemnation, given that you'd have to condemn almost every tribe and nation that has ever existed.