I think the main complaint is Xmas instead of Christmas. There is Hanukkah, but no Xkah. There is Ramadan, but no Xdan. There is Panchmukhi Ganapati, but no XGanapati. Why is Christ, therefore, X-ed out of Christmas? It certainly isn't length or spelling, given that the Panchmukhi in Panchmukhi Ganapati is far longer and more complicated than the whole word of Christmas. No, Xmas is a slight against Christ, no other way to interpret it, and quite frankly I think Christians are sick of being singled out this way.
Don't bother bringing up what Christians did in centuries past, we all know what was done and there's never been a religion where someone hasn't done horrible things in its name.