One reason the JWs don't celebrate Christmas, besides the fact it's supposedly an insult to God, is that they purport that it's wrong to "lie" to children by telling them Santa Claus exists.
I really didn't give the issue much thought until recently. The JW I used to study with called me and asked how I was doing, and we eventually got on the subject of Christmas, and he brought up that it's wrong because parents lie to children by saying Santa Claus is real.
I guess he has a point, but on the other hand I really don't know about any cases where a child was traumatized because he or she discovered Santa didn't exist. Heck, I remember as a little kid, some of my friends in the neighborhood figured out it was parents, and they didn't seem to mind. I didn't care when I found out he was fake either.
I guess the question is: Is it okay to lie if it brings joy to a person?