Just curious-and not being snarky, I promise-but it seems to me that Christmas is a Christian celebration of the birth of Christ, yet atheists and people of non-Christian faiths choose to celebrate it as a "secular" holiday, which it isn't. Yet you never hear of atheists choosing to celebrate Chanukah or Ramadan or other non-Christian celebrations in a secular way. It just strikes me as odd and sort of a double standard.
Pretty much every culture in existence has come up with a way to have a nice celebration of food, light and good cheer somewhere around the winter solstice where the days are short and everybody could do with a bit of a boost.
Early Christians took elements of older pagan and Roman festivals and beliefs and incorporated them into Christmas to make the transition easier. You'll notice that there are no mentions of Christmas trees, turkey dinners, yule logs etc. in the bible, and no indication that Jesus was actually born on the 25th December.
For lots of non religious people in western countries, Christmas is celebrated as a mid winter cheer up festival, a chance to enjoy good food and drink with good friends and family, a time to have a day off work and do a little celebrating when its otherwise cold, dark and generally depressing. It makes sense to do this at Christmas rather than Eid, Diwali or Chanukah as its a national holiday, the logistics are easier and Christmas is part of their culture even if its not part of their religion.
Neither way of viewing Christmas is more right than the other.
(I do actually celebrate Diwali in a non religious way by attending the awesome fireworks display in my city.)