Apparently Atheists do it because it's a cultural tradition. Nevermind that that cultural tradition comes from the very Christianity that they reject.
Apparently it does bother you or you wouldn't be whinin' about it.
You do have a point however. There are various pagan celebrations that were "baptized" by Christianity. All Souls and All Saints day are other examples aside from Christmas. It's a date on the calendar and it's meaning is the same as well as the added meanings of the pagan tradition. The remembrance of Christ our light Who came into the world at the same time the days begin to grow longer is very apt if you ask me. Jesus didn't have to be born on that day for us to celebrate it at that time.
The large majority of "Christmas traditions" are indeed pagan ones. Honestly, as a Christian it doesn't bother me one whit. If it's not antithetical to the basic tenants of Christianity then it's harmless. Christianity is full of "paganism" (whether Protestants want to admit it or not); it's a melding of Judaism and so-called paganism.
I think the point of the OP was, why would someone like you mAlice celebrate Christmas in your home (hey, maybe you don't I don't know)? If you do, I'm sure it doesn't center around Christ so why don't you just call it Sol Invicta(Ancient Roman) or Lenaea (Ancient Greek) or Bodhi Day (Buddhism) or Yule (Celtic Druids and Neopagans) or Inti Raymi (Ancient Incas) or Shabe-Yalda (Zoroastrainism) or Soyal (Hopi Indians) or The Long Night (Vampyres) or simply Winter Solstice?
Btw, did all of these peeps steal from each other like you accuse Christianity of doing?