I suppose the argument is more ls why is it a holiday many have off for (forced to celebrate). Look at a calender there is always somthing under national recognized days, weeks, months (yes there is a national ice cream day). As we are the land of the free and PC tolerant of just about everything I think it remains as it really dosent hurt anything and would cause more of a stir getting rid of a tradtion. Never can all the people be pleased at the same time.
I think it started out as a reminder to the history we are taught as I was not around back then I can not say which argument that has sprung up about Columbus is actually true or false. For that matter who the first person was toactually "discover" a large land mass that already had homo sapians on it to begin with.