If you look at the historical record, you will see that Columbus himself was responsible for the murder of many people.
The grade school image of Columbus as a hero is not simply naive; it is wrong. Columbus did not have a character worthy of aclaim. He was of humble birth, had little education, only held small jobs, factors which in and of themselves are not negative. Columbus did travel and read, but most of his information had more to do with tall tales than scientific fact. He was wrong about some very basic things--such as the size of the earth. But more important was his authoratative nature and his unwillingness to consider the interests of others. He was greedy, and took the reward for discovering land in the Caribbean for himself (although it rightfully belonged to a crew member). He was egotistical and over dramatized his achievements (seasoned sailors were used to traveling away from land). He was a bad administrator and experience taught him nothing.
In the Caribbean the Arawaks greeted him, but Columubus responed by demanding gold and enslaved them. He kidnapped 10 to take to Spain; one died soon after getting there. On his second trip he promised the Spanish crown slaves & gold. He demanded gold of the Arawaks, and when he couldn't find it, he resorted to capturing slaves for both sex & labor. The people fled from the Spanish, and Columbus found empty villages. The exploration turned into a military campaign with 200 soldiers and specially trained people-eating dogs which decimated the population. Columbus captured 1500 men, women, and children. He sent 500 to Spain & 200 died on the voyage. Columbus is DIRECTLY responsible for the deaths of thousands of Arawaks in Haiti. He forced them into gold mines for 6-8 months and 1/3 died, exhausted, depressed, ceased to procreate, killed their infants. Columbus also killed them thru murder, mutilation, suicide, overwork, abuse, and diseases.
The following history is one of depopulation: a heavy toll from wars of resistance, hard labor, and malnutrition. In 1492 there were 3 million people on Hispanola. Two years later the population was cut in half. In 1515 it was down to 50,000, in 1550 it was 500 and by 1650 there weren't any left. Furthermore, Columbus' actions launched an era of modern colonialism, rape, pillage, genocide, cultural destruction, slavery, economic & environmental devastation.
To celebrate Columbus is, as one Guatemalan has noted, the same as having Jews celebrate Hitler and the holocaust. Columbus is much more than a representation of evil; he is the very embodiement of that evil.