To be fair, he IS responsible for sparking the European conquest of the New World, and for all intents and purposes, he WAS the first. Sure, Ericson was there earlier, but that's like saying Martin Luther didn't start the reformation because Jan Hus had a similar movement decades earlier. Columbus's voyage had literally trillions or quadrillions of times the impact as Ericson's trip. One left behind an interesting historical footnote, the other changed human history in irrevocable ways.
Whether you like what he (and smallpox) did to the natives, at the very least, his actions are directly responsible for or indirectly contributed to:
-The creation of EVERY state in Western Hemisphere, where a majority of Western Civilization now resides, including the richest and most powerful country in the world.
-The rise of the triangular trade, which enslaved million of Africans, set up large-scale plantations the likes of which had not been seen since Roman times. Combined with modern shipping and bookkeeping, they formed what was, to that point in time, the largest commercial enterprises ever seen.
-Providing a place overseas to ship off religious dissidents, "surplus" population, and providing for the creation of some of history's largest empires.
-In a lesser achievement, Columbus also was the first to navigate the Ocean for that long and that far, going a very long time before seeing land.
-He also initiated the Columbian exchange of crops, livestock... and diseases... from one hemisphere to another. Cattle, wheat, and pigs were examples of crops shipped into the Americas, while corn, tomatoes, and turkeys were shipped into Eurasia and Africa.
-Most indirectly of all, Columbus's achievements would one day enable Western countries to grow in a place that did not have entrenched nobilities and monarchs. Even though they had a king, he was thousands of miles away, across the ocean, and given the changing intellectual climate, it was much for nobles to stake claims in the new world, where many people would later run in order to escape being serfs or tenants on a farm (given how many Africans were enslaved here, this is ironic, but it DID mean new land for European settlers.) In the long run, this contributed massively to the formation of republics in the new world. No Columbus means no colonies; no colonies means no George Washington or Simon Bolivar.
I'm not saying that you have to like what he did, but his impact, both direct and indirect, is massive. Not every great individuals gets his due; fewer people in America know who Constantine the Great is than they know who Babe Ruth was... and the former is responsible for legalizing Christianity! So basically, like it or not, we really should recognize Columbus's impact.
EDIT: Yes, it probably was Amerigo, but Columbus was there before him.