fwpc3 pointed in the right direction by offering the link to Wikipedia regarding the use of X in Christmas.
I guess I might be classified by the OP as a "religious freak" but so far I think I've restrained myself pretty well.
My BA degree from Stetson University (back when it was affiliated with the Southern Baptist Church) was in Liberal Arts, heavy in religious and history subjects, including even a semester of the Greek language. I abandoned it after one semester because I was taking German at the same time and during every Greek test the answers came to me in German. But, I digress.............
If you were to examine the handwritten notes that I made during lectures in religious classes you would find an X every time the word was "Christ." And if the word was "Christian" you would find "Xian." It was simply faster to take notes in this manner. I'm sure many of my fellow students did it too.
Those of you in the "high churches" where priests or pastors wear robes and use highly decorated Eucharist utensils might be familiar with the Chi Rho symbol. It is a Chi, written in Greek as X, and Rho, written in Greek as P, with the two overlaid. It is the generally accepted symbol that is to be read "Christ." The letters are transliterated into English as Chr, the first two letters for Christ in Greek. See the photo below.
Having said all this (it might have been shorter for you to have read the Wikipedia article) the point is that using X for Christmas historically is not an attempt to take Christ out of Christmas. When I see Xmas written I read it in my mind as Christmas.
However, I join the majority of posters here in preferring to see it written MERRY CHRISTMAS.