I was brought up Catholic, but Catholicism and Christianity and I parted ways a long time ago. Actually, theism and I parted ways a long time ago as well. I'm just not a faith person. Some people's brains work that way. Mine doesn't.
I'm always tempted to say that Christmas should be left to Christians. In origin, it was a celebration of the birth of their christos, their anointed one. It doesn't matter that the Church intentionally set the celebration to coincide with the midwinter feast of other cultures (notably the Roman Saturnalia). The meaning of Christmas itself is still the nativity, the birth of the Christian messiah.
Of course, Christianity has always been evangelical. From the very first, it was about telling others of their "good news." So it would only make sense for Christians to want to share their midwinter celebration with the world. Even if non-Christians celebrate it differently, Christians can say that it's all part of the same celebration.
Even beyond Christian evangelism, the narrative in the Gospel of Luke contains universal themes. Unlike the author of the Gospel of Matthew, the author of the Gospel of Luke wanted to reach out to "the nations." His messiah didn't come only for the Jews. He came for everyone. And to go along with that event, we have a night of peace, of song, and of universal brotherhood (and sisterhood, we hope). The first outsiders to see the baby are poor shepherds. It was the Pax Romana stood on its head.
So even though my midwinter celebration is not about Jesus, I will happily celebrate along with believers and nonbelievers alike. There will be light and music and food and generosity and love.
Happy Christmas to you! Here's my favourite non-sacred Christmas song: