It doesn't matter how it originated, it only matters what we make of it.
Today, we consider Christmas a season to be charitable, to be kind, to share with others your joy, and to "do good" so as peace and joy come more frequent in the days to come.
I am non-religious. To me Christian or not really doesn't matter. I liken it to a neighbor celebrating a new grand child. It has nothing to do with me, I haven't seen the kid and likely never will. But, I share their joy, I celebrate with them and wish them best.
I use this occasion to wish everyone a Merry Christmas. I wish all a joyful time now, and more joy to come. If you believe, great. If not, we all know laughter and joy are contagious - nothing wrong with spreading it so everyone having a joyful time.