We have discussed this at length over the years here. But I wholeheartedly agree with you -- Christmas is for everyone.
I would encourage you to study the origins of Christmas, especially when it comes to the idea that Christians adopted pagan symbols and traditions. A lot of people assume -- even Christians -- that Christmas doesn't pre-date Christ, and yet, the Old Testament clearly does. Consider the words of Messiah, commonly performed each Christmas, "...and His name shall be called Wonderful, Counselor, the Mighty God, the Everlasting Father, the Prince of Peace..."...those words are from Isaiah which are, of course, from the Old Testament.
That begs the question...where did the "pagans" get their traditions?
Of course, ancient thoughts and origins are one things.
Contemporary feelings, spiritual exploration, etc are quite another. Many are the reasons for one to chose atheism over other belief systems. That's a personal thing.
But Christmas, for whatever reason you celebrate it, is celebrated here and ALL are welcome. I hope EVERY point of view is explored and shared. That is part of what makes Christmas such a part of our lives here.