I think Christmas is no longer just a religious holiday. I believe in god but I know several atheists who celebrate Christmas and some of my Christian friends (but not all of) do not think they should be celebrating if they do not believe in Christ. I believe it has gone past that to just a holiday to come together and show each other we care.
Edit: If you read what I said: I think atheists should, do and can celebrate Chirstams.
Edit: If you read what I said: I think atheists should, do and can celebrate Chirstams.