I know that I'm a bit late with this, but we moved house and didn't have the internet for two weeks! Celebrations such as Christmas and Easter have a big non-Christian element - the Christmas tree is more to do with Yule, for example, and the Easter egg is more to do with the re-birth of nature in spring than anything to do with religion. Hallowe'en, on the other hand, is obviously directly linked to All Saints Day, and if you believe that it's a celebration of evil spirits, then evil is a religious concept - as an atheist, I don't believe in evil. Also, the celebration of Hallowe'en seems to come from the US, where they're much more religious than us. I therefore propose that Hallowe'en is actually the most Christian mainstream celebration that we have, and that could well be why it makes me so uncomfortable.