The absurd it-isn't-in-the-Bible stance has caused all manner of legalistic misery. When encountering such people, I suggest - sometimes mildly, and sometimes a bit more forcefully - that Christians are free to do anything not prohibited in the Bible, and that therefore celebrating Christmas (not to mention weddings, graduations, birthdays, etc) is perfectly fine. I say this as someone whose parents were in a cult that frowned up Christmas and much more besides (thankfully, said cult collapsed when I was seven).