I don't want to sound mean, but you have to see it from their perspective... .
Maybe it is not important to you, but it is important to them. It is kinda selfish to not let them do it simply so that YOU feel better. It is their event, the least you could do is respect their practices. If you want to tell them that they don't need to do it, then fine. However, to threaten to kick their ass for it? That's a bit extreme.
Think of it this way: If you don't exchange gifts for Christmas, then fine. However, you should still at least accept a gift if one is given to you. Why? Because you accepting the gift is important to them. There is no need to kick their ass for giving you a gift.