Instead of writing a long tirade about that which others have already covered, I'll just link to a post already written by someone else about the same thing.
Suffice to say, Christopher Columbus (aka Christopher Colon) is nothing to be celebrated really. He was a tyrant who tortured, raped, enslaved and murdered natives on numerous continents to further his own agenda.
Read the post by Rhapsodyinbooks if you are unfamiliar with his history and his legacy. Then you decide whether he is a cause for celebration and a national holiday.