The paradox of tolerance [1] is a PITA. At the end of the day a santa hat is no big deal, but by the logic of "even a single person being offended is one too many", taken to the extreme, all that is left is the lowest common denominator of what all humans tolerate (if there is such a thing).
On a more practical note, I find it hard to reason on how deal with issues like this. It's like if you try to be level headed, avoid conflict, and try to see things from the other side you already lost, because there is no corresponding empathy coming from the other side. The only solution is to give in, or deal with an offended internet mob.