Columbus Day or Native American Day

Why do we even have Columbus Day?! Columbus and his cronies were murderers in every way possible....
He did not discover American; he invaded it w/ his European sailors. He brought disease to the New World like scurvy. When he and his fellow sailors tried to bring back the Indians back to Europe, he ended up killing them. When he got to the New World, he killed the Indians by chopping their hands off and scalping their hair off their heads.