There is a difference though in judging history with the benefit of what we now know in our later and more enlightened existence and in judging a person by the standards of their own time. Unless we look through the eyes of those who were living their own history whether it is Biblical figures or Roman emperors or those who lived the exploration of 'new worlds', who lived the Reformation, who lived the Renaissance, etc., we will not understand their perspective and we will not understand their history accurately.
Columbus has much to commend him and much to condemn him as did almost all other people of history. So many figures have been heroes and men/women of great accomplishment while also being deeply flawed individuals or subject to serious error as we now know. Who among us can say he/she is not the same?
Columbus was very brave to sail off into the unknown with three small ships, most especially when both the Church and science taught that there was an edge out there to be sailed off of to the almost certain detriment of any who did so. He remained convinced until his death that he had discovered a route to an edge of Asia and he never knew that he had found 'the new world'. Yes he took slaves that that was common and quite legal in Europe at that time--humanities conscience had not yet developed to the point that slavery was in any way immoral. And yes he was a ruthless and very unpopular despotic dictator of Santo Domingo even as he made friends of indigenous population on other Caribbean lands. Yes he and his men carried deadly diseases to the new world, but that was not intentional and it would have happened eventually anyway.
So to be fair to Columbus, he was a man of both virtue and feet of clay, honor and greed, loyalty and self serving ambition as most people are in some way. Did he merit his own holiday and to be memorialized in the names of cities, monuments, countries? Probably not as much as some others would have been, but he did leave a definite mark upon history and, for better or worse, he did further the advancement of knowledge and civilization.