Hell, I've seen it celebrated by non-Christians in non-Christian countries; I've been abroad in Asia over the Christmas season a couple times in the past, and, you know, seeing a Christmas tree in Thailand is sort of a bizarre sight, but there's a reason I've never thought of it as a specifically religious holiday. I've just -- I've never had that argument thrown at me before, so it was a very bizarre experience. (And I think I know why, or at least part of the reason why, my family celebrated Christmas without being Christian, now that I think about it. During one of my grandmother's flip-flopping of Christian denominations, she stumbled onto the one where you don't celebrate any holidays whatsoever, and that made a big impression on my dad, I believe.)

I can kind of see where she was coming from, I guess that if you've grown up with something being a specifically religious holiday, the idea of taking said religion out of it must be mindboggling.