In my opinion, we should be Christian to celebrate Christmas.
Nowadays a lot of people celebrate Christmas, because : Christmas Tree, Santa Clause, Presents, official supper, time only for family and rest. Advertisments, decorations and all around us are connenced with Christmas.
Christian prepare to this event. They take part in Adwent ( they go every day for 4 weeks to church to the Mass) and they wait for birth of Jezus Christ. It is one of two the most important event in Christian calender.
Every religion has got own events and we should celebrate only own.