Well i haven't really read much of this topic at all(too many pages)
But for one.. Christmas is not even a Christian holiday. Its a Pagan holiday. The christians started christmas as a way to convert the pagans to christianity. Same with a lot of the other christian holidays(if you notice, they are all on or around pagan holidays). The only difference between the Pagan holiday and Christmas is Jesus.
If an athiest were to celebrate christmas, it should be more in the pagan tradition. I'm not athiest, but I still don't celebrate christmas, mostly because christians are full of ****.