There is no reason as a Jew that you can't celebrate Christmas, I'm an atheist that despises religion, and I do it. Why? Because Christmas is not, nor has it ever been, a Christian holiday. December 25th was a day of pagan celebration, until the Roman empire decided to choose a single religion to mind control the population, at which point they kept the same day but changed the label. Today, it's just a commercialized tradition. According to scripture, it is not possible that Jesus was born on December 25th, which is why some Christians I've met don't even celebrate Christmas. The Christmas tree, mistletoe, gift giving, etc. are all from pagan tradition. I celebrate Christmas because most people that know me are aware that I am an atheist, and I know the topic always comes up about "Why do you celebrate Christmas if you think the bible is a myth?", and I get to explain that Christmas has nothing, and never has had anything, to do with Jesus. The "reason for the season" was and is still about mind control, whether it is religion or getting people to go out and buy a bunch of crap. You also get to make your kids happy if you have any, and that is a big gift in itself.