Why do atheist love Christian stuff, eat it all up, then hate on it, gosh darnit?

Aren't religious and cultural mores like fashion and dressing up. Yeah, they may not be necessary, but they provide a zest for life. Everything from Christmas, to the western traditions of marriage, I mean even gay marriages have a wedding ceremony that mimics a Christian. I don't think an atheist could come up with their own cultures. Can an atheist come up with a cooler and more meaningful holiday than Christmas? If I were atheist I'd celebrate Christianity the way I celebrate... Americanism. They are both so closely tied together, don't ya think?