Having holidays is a way for people to relax and remember the ages before the Traveler. We are still on earth and there are still earthlings so they would carry on traditions. On the "political" side, people who say no usually say that it's disrespectful for other cultures. It's an American made game. American holidays. Nuff said bought that. Bungie could brainstorm holidays similar to ours that they could create. So it's not Christmas but it's similar to Christmas so as to not disrespect other cultures if they feel they would be. i.e- instead of calling it Christmas, call it "The Light Day" something referencing the Traveler. Since he gave us stuff like in Christmas.