My colleague, Dennis Byrne, here at ChicagoNow wrote an excellent article on Rahm Emanuel's "inclusive" and "welcoming" decision to call the Christmas tree in Daley Plaza a "holiday tree."
"The use of the Christmas tree is relatively modern. It's origins are found in the medieval mystery plays that depicted the tree of paradise and the Christmas light or candle that symbolized Christ, the Light of the world." - From December's Magnificat
The word Christmas in English means "Christ's Mass" and in Latin it means "The Birth." Even the word holiday means "holy day."
I believe I have a unique perspective on this since at one time I wasn't a Christian, but I did celebrate Christmas. Sort of.
At a very early age, I discovered there was no Santa. According to my parents, I was three years old when I caught them putting presents under the tree and I wasn't buying the excuses of why they were putting the presents there and not Santa.
We didn't go to church because my dad was a divorced Lutheran with children and my mother a Catholic. In those days you didn't get an annulment. Religion was not part of our family dynamic.
But all through those years, I still called it a Christmas tree and so did everyone I knew including those who were not Christian. For the non-Christian, it was a gift-giving holiday not a religious one.
If you're not Christian, but you celebrate with family and friends, that's fine. But to those of us who celebrate the birth of Christ, the Light of the world, it's a Christmas tree. Period.
What it boils down to, is that in our current culture it's okay to "exclude" and "unwelcome" Christians even from their own holidays.