I grew up celebrating Christmas in a family that became openly Atheist when I was about... 10, maybe? So it's Christmas. And if I have kids, they will probably celebrate Christmas as well, even though it makes no sense for them too. (Perhaps "Rampant Consumerism Holiday Season", a great spread of gluttony and purchasing that goes from Thanksgiving through New Years.)

My dad's been listening to Free Thought Radio and reading the Freedom From Religion newspaper a lot, though, so he's started calling it "Winter Solstice Holiday" as of this year.