In America, we've recently been in a pattern of feeling guilty about everything it seems, even if it is distant history.
We celebrate the adventurous spirit of Columbus who set forth into the unknown and "discovered" America. Obviously, from earlier Nordic explorers to Native Americans who apparently may have arrived earlier via land bridges from Asia, there are many ways to criticize this perspective, often in favor of a preferred perspective rather than an objective one.
One open question is what really matters about who was here "first". But in order to have an argument, you have to create an issue. So, simply, a day in honor of the adventurous spirit in people is now used to continue childish arguments.
Not being risk takers anymore, we focus on the negatives of the outcome of Columbus' arrival, which had very little to do with Columbus of course. That is a result of cultural behavior and many people's choices.
The same distortion happens now with holidays referring to God, giving thanks, newer holidays celebrating ethnic heritages, military events, and so forth. If you have had a friend who can find the problem in every opportunity, you know the feeling that we have in America these days.
The one benefit of this overdone cynicism is that we are aware that history can be written many ways. Unfortunately, what has happened is history gets rewritten from the new guilt-based perspective, and is no better than before. But it gives people something to fight about, which is very popular here now also, as you can see on television shows here from "Survivor" to "Maury" and "Dr. Phil", even at times "Oprah."
So, if you wish someone well on the wrong holiday, or in the wrong way, they now have the excuse to behave rudely towards you for no other reason than your greeting! How strange.