What makes you think christmas is a pure christian holiday? What has a fat guy in a sleigh to do with christ? Surely, christians think it's about the birth of Jesus, but that is just a part of it. Why do we celebrate that fat guy, and jews do ghanouka (or whatever).
Santa Clause has evolved from Saint Nicolas, a saint that in his time helped a lot of children, and therefore got the reputation of a friend of the children. He also had freed a slave from Turky in his lifetime, which followed him for the rest of his life. In our country we have a holiday with that guy and he still has a fleet of black guys who give out the presents.
So christians do not have the primairy right on christmas. Christmas are just a lot of holidays from different paradigms in the world which has evolved in it current state. There is even proof Jesus was born on a different day, but the dates were changed to comply with the Heithen holidays.
So why do americans ban christmas trees? this is just nuts.