What's wrong with Saying Merry Christmas

I don't know why certain people object to the phrase Merry Christmas, and I don't understand why they would use the word x-mas instead. Although I am Jewish and do not celebrate Christmas, I am 100 percent in favor of people saying Merry Christmas and singing Christmas songs in public. This is a free country, and freedom of religion. I know that I would not like it if non-Jews were to tell me not to use the word Passover or the phrase Good Shabbos because it would offend people. Because some of my father's relatives were killed in the Holocaust and because my maternal grandfather saw his sister killed in a pogrom in Czarist Russia, I'm so grateful to live in a country where there is no Anti-Semitic legislation. Let the Christmas lights blaze and blast the Christmas music. With that said, Merry Christmas to those who celebrate this happy holiday.