Yes, Christmas is my favorite holiday. Many atheists enjoy the Christmas holiday, and many choose not to participate in it. To me, the holiday is about getting together with family to recognize that family is important. This sentiment has no ties to Christianity or any other religion, and yet it is the essence of what we think about when we think about Christmas today.
When people are asked what they think of when asked about Christmas they think of:
Gift giving and receiving
Lights on houses
Stockings by the fire
Birth of Jesus
Most of the things we think of have nothing to do with Christianity. In fact, the holiday as we know it originated in retail. Good, pious Christians historically, from the years 1000 to around 1850 did not celebrate Christmas, and often Christians such as early Americans and the Church of England banned the celebration of Christmas, because the celebrations were generally filled with violence and debauchery. When Christmas started becoming popular, it was because retail stores began spreading stories equating Christmas with gift giving.
Therefore, the “Reason for the Season” has never been about the birth of Jesus. Only in the last 50 years or so have Christians started pushing to make the season have something to do with Jesus.
If you take the non-Jesus things out of Christmas, the holiday would probably not be celebrated much. If you removed gift-giving, family get-togethers, Santa Claus, Christmas Trees, Lights on houses, stockings by the fire, and reindeer, then the holiday would go away, or become about as popular as Ash Wednesday.
Finally, how do I know it is a secular holiday? Well, the holiday, as it is celebrated today, originated in the United States. And the United States is a secular nation, our constitution prohibits us from endorsing any particular religion. Yet, in 1870, the United States declared Christmas to be a National Holiday; thus Christmas is a secular holiday.