Only Christians allowed to celebrate Christmas?

After all the War on Christmas brouhaha, I have to admit, this was one I'd never come across before.

On another message board I frequent, a woman complained bitterly about "these non-Christians who claim to celebrate Christmas". I explained to her the basic history of solstice/Yule/Saturnalia celebrations, that the timing of Christmas was originally chosen to capitalize on existing mid-winter festivals, and that most non-Christians who celebrate just think of it as a time to focus on friends, family and charity.

She came back and said that would be like if she chose to celebrate Passover or Diwali as a time with friends and family, that she still didn't see the point.

I said that Christmas is nearly ubiquitous in American culture, and most of us grew up celebrating it, and may still have family who are religious and celebrate the holiday with that in mind -- family who would be disappointed if we stayed home. I said if she had grown up Jewish but no longer believed, she might indeed still attend her family's seder to spend time with them, or even host her own to teach her children about their heritage, if not any religious beliefs.

I said that ultimately, for me, I celebrate the solstice and don't have a problem with calling it Christmas, because after all, the common English name for the holiday where Christians celebrate the resurrection is Easter, after a pagan fertility goddess.

She pretty much ignored that, and continued to insist that we had no right to the name "Christmas", because after all, "CHRISTmas", yada yada... I gave up at that point.

I'm thoroughly confused. Folks like this want all cashiers and bank tellers and waitstaff they encounter in December to ONLY say "Merry Christmas"...but apparently no one is allowed to celebrate Christmas unless they believe in the literal truth of the nativity?