Yes we celebrate Christmas. There isn't any moral dilemma. The tree, the food, and the presents, are all secular. But honestly I don't really care, we have angels on the tree and I have a New Mexican creche. We have read a Christmas Carol out loud. Tradition and belief are not synonymous.
If there is a god, I want to believe that there is a god. If there is not a god, I want to believe that there is no god.