I think people hate Christmas because they know they are supposed to be happy. It amplifies our misery knowing that we should be having a good time. Suicide and depression ratings both go up at Christmas. I'm personally not a huge fan myself, and I have had bad luck for the last 6 years over the Christmas period, breakups, deaths, crushing depression and abandonment being the main themes, but it seems to be enjoyable so far this year.
Although the music is killer. I work in a restaurant, and we have the same twenty songs over, and over, and OVER again. For two months. I love the Pogues, but now Fairytale of New York makes me want to hit people. To be fair though, that's work's fault, not Christmas.
And as much as I hate Christmas, watching my Mum open her presents from me always makes me happy that it exists. Girlfriends come and go, nieces and nephews grow up and become as jaded with the whole thing as myself, but a Mum is for life.
Besides, you can always just get really drunk.