Though the holiday of Christmas has its roots in Christian tradition, it has evolved to become a celebration that can embrace all humanity. Christmas stands for love, brotherhood and family. These values are important for all cultures. If the celebration of Christmas reminds people to be kind and loving to others, then it is a tradition important to all humankind.
Christmas is hardly a religious holiday related to the birth of Jesus. Modern Christmas celebrates presents, Christmas trees and Santa Claus, none of which refer to Christian elements. Therefore there is no logical reason to prevent non-Christians from celebrating Christmas, given that it has become a more secular holiday than religious holiday.
Christmas is more than just a Christian holiday. It has become the accepted tradition for many different religions and non-religious types. Since Christianity is the dominant religion in the United States, even those who do not affiliate with a particular religion know the traditions, songs and customs of Christmas and choose to celebrate the holiday.
Yes, Christmas has become a universal holiday. From a Christian perspective, the holiday celebrates the arrival of the Savior. Who wouldn't want to invite everyone to hear about that? From a broader cultural perspective, Santa and the Christmas tree have become a full-fledged part of society, both inside and outside Christianity, and so the entire culture should be able to celebrate the holiday.