Celebrating Columbus is about celebrating the occidental culture arriving to America, a jump of 5000 years for the current level of development of people living in America in those days. A tremendous progress from non literacy and agricultural tribal culture to a strongly developed pre capitalist one, thanks to which America and the world are what they are. 
On the other hand there is nothing like “native” people really, all pre-Columbus residents arrived in several migrations most, but not all, of them through Behring “bridge”. While spreading through the continent those tribes imposed ones to the others; slavery and genocide were a constant. The clash with the Europeans in XVIth century , although not pacific or perfect, was more civilised since Europeans applied their medieval rules and codes ; American “natives” were not treated worst than European feudal servants of the time.