The complaint about secularists "taking Christ out of Christmas" is a common one today and a rallying cry for Christian Nationalists who promote the War on Christmas. Many religious conservatives say that liberals are trying to take Christianity out of Christmas, but should Christianity even be in Christmas to begin with? There are Christians today who say that it shouldn't. This position used to be much more common and maybe it's a sign of the influence of modern culture that things have changed so much.
Christians need to pay attention to the fact that modern celebrations of Christmas simply don't have anything to do with Jesus, the Feast of the Nativity, or the Incarnation. Consider some of the most popular Christmas traditions: erecting and decorating a tree, hanging wreaths, sending cards, drinking eggnog, giving presents, hanging mistletoe... where is Christ in all of this? Most of it is pagan. It's no wonder that many Christians throughout history have objected to Christmas celebrations. At one time, celebrating Christmas was even illegal among the Puritans.
Keep in mind also the fact that it is Christ-Mas -- this was a time for a Mass celebrating the birth of Christ. How many Christians today actually continue to do this? How many worry about the fact that the Mass was taken out of Christmas? It's difficult to take seriously the complaints about taking Christ out of Christmas when so few of these same Christians raise a peep about all of the other religious aspects of the holiday having dropped away over the years.
The increasingly Christ-less nature of Christmas is due to the same forces which have stripped the holiday of its other religious features: in an pluralistic country where non-Christians are adopting the holiday as a secular and national one, it only makes sense to try to appeal to the widest possible audience. The secular symbols of Christmas are more popular than the religious ones because more people can identify with and accept them. It's not a conspiracy, it's simply the natural product of a culture that is becoming both secular and religiously pluralistic.
The above image is taken from a World War I poster calling on men to join the army and help hold back the "Hun," depicted menacing a helpless woman and child. Here the Hun has been replaced with Christ, a symbol for Christian Nationalists menacing secular society by held back by those who join the War on Christmas.