Massachusetts liberals have been at it a long time:
The Puritans considered Christmas un-Christian, and hoped to keep it out of America. They could not find Dec. 25 in the Bible, their sole source of religious guidance, and insisted that the date derived from Saturnalia, the Roman heathens' wintertime celebration. On their first Dec. 25 in the New World, in 1620, the Puritans worked on building projects and ostentatiously ignored the holiday. From 1659 to 1681 Massachusetts went further, making celebrating Christmas "by forbearing of labor, feasting or in any other way" a crime.
That's from an NYT article on the commercialization and politicization of Christmas. Let's face it: what people do with holidays is their business. Bill O'Reilly can feign outrage all he wants, but it does not make any sense to do so. As for the validity of the December 25th date, since the Western calendar is defined around the life of Christ, 12/25 is Christ's birthday, by definition. There is no sense in arguing about that.