Well, "Christmas" isn't Christian anyways.
There is no evidence that Jesus was born on Christmas day. It's more likely he was born in another season, if he lived at all. But Christians placed his birth on that time, which was celebrated by earlier pagan traditions, like Yule. In Denmark, for example, Christmas is called "Jul". Christians hoped to take advantage of the existing traditions to gain more followers, but the truth is that "Christmas" was hijacked by Christians. It's ironic that some Christians are angry when it's losing it's "Christian roots".
So happy holidays/Winter Solstice/Yule or whatever, everyone. I'm definitely an atheist, but I celebrate Jul anyways.
Still, Christians have managed to spread this myth everywhere. The media is always effective for that. Here's that popular Charlie Brown cartoon remade: