There is no governing body, and there are no bishops, elders, or anyone else determining how atheists should do anything, or telling us what to believe. So how, or if, atheists decide to celebrate Christmas is entirely up to us.
There are many options. The first is to not celebrate Christmas as a commemoration of the birth of Jesus at all because as atheists, of course, we do not believe there is a God, and therefore the term son of God is nonsensical. (Of course, Jesus never claimed the title for himself and called himself the son of man anyway.)
There are some atheists who doubt Jesus ever existed, while others accept he existed, with the stories embellished and altered for the purposes of those writing them. If Jesus did exist, there is little doubt he was an enormous influence on those who heard him preach, and his teachings can be rated among the greatest teachings in the world’s history. So why not celebrate his birth? (Of course, it would then also make sense to celebrate the birth of other great teachers of the past such as Mohammed and Buddha.)
Another option is to accept that the modern Christmas has little or nothing to do with Jesus anyway and that it is mostly a selling opportunity for businesses and corporations. Every trick in the book is used to pressure people into spending as much money as possible in the ‘holiday season’. If an atheist can find something to celebrate among the rampant consumerism, then they can celebrate it by loading up their credit cards, the same way Christians do.
A third option is to accept that Christmas has always been more to do with pagan traditions than with Christmas and that almost all the traditions of Christmas have nothing to do with Christianity at all. Evergreen trees and holly were symbols of the winter festival long before Christianity since these plants did not lose their leaves and appear not to ‘die-off’ during the long northern European winters. Similarly, the Yule log is part of a Nordic festival of 12 days of general feasting, partying and drinking, probably in honor of Yolnir, who was later called Woden and then Odin.
Christmas, just a winter festival
Christmas is basically a winter festival that was hijacked first by Christians, and which has since been hijacked by greedy capitalists out to make as much money from it as they can.
Christmas is more concerned with the winter solstice than with the birth of a baby 2000 years ago. It is rather odd that Christians celebrate the birth of Jesus anyway since they normally celebrate the death (especially martyrdom), such as those of the saints, and of course, Jesus. Winter festivals have long been connected with birth – the birth of the invincible sun, Natalis Solis Invicti – the name given to the celebrations in 274 CE by pagan emperor, Aurelian, in a year when the winter solstice fell on December 25th. The winter solstice was also celebrated by many other pagan groups in Europe, and the celebrations included those of Mithras, the sun. In the darkest, shortest days of winter, the return of the sun and longer days was celebrated.
So what are Christmas celebrations anyway, and can an atheist celebrate Christmas without being hypocritical?
Personally, as an atheist, I usually have a pagan Christmas because it is a family and cultural tradition with no basis in fact, and because I normally spend time with family who also like the pagan aspects of Christmas, such as the tree, holly and exchanging gifts (although some belief the Christian story too).
Christmas has almost nothing to do with Christianity anyway. People give me gifts at this time of year, and I enjoy giving them gifts too (although I try to make them meaningful rather than buying into mindless consumerism). None of this has anything to do with religion, since the giving of gifts preceded the Christian hijacking of the winter festival and was a large part of the earlier festivals such as those in pagan Rome that was held from December 17 to 24, in which people had a holiday from work and exchanged gifts. The giving of gifts at Christmas has nothing whatever to do with Jesus or wise men bearing gifts. Of course, there is no reason for atheists to celebrate pagan festivals any more than religious festivals. But we can if we want to.
I also celebrate at this time by having a break from work, since Christmas is as good a time as any to unwind, catch up with family and friends (who are mostly on holiday at this time of year), and time for parties and get-togethers. There’s really no reason why atheists should feel they need to forgo these festivities if we don’t want to.
As free thinkers with nobody telling us what to do, think and believe, atheists can celebrate Christmas if we wish, and however we like, or we can just ignore it as most of us ignore the other pagan festivals. Perhaps a more interesting question is how should Christians celebrate Christmas?