Greg Lake's "I Believe in Father Christmas" is obviously a "Christmas song" due to its subject matter, but it's seriously anti-Christmas, specifically the excessive commercialisation of Christmas.
Pete Sinfield is on record as saying his lyrics are about the loss of innocent childish beliefs, and equates his realisation that Father Christmas doesn't exist with his (not much) later realisation that Jesus wasn't who people say he was either.
The song is not (necessarily) anti-Christian, despite the second verse, but it's certainly anti-Christmas... Great song, though, thanks in no small part to Prokofiev.