I don't care if Jesus was born sometime in the Spring.
I don't care if the early Church appropriated the Roman festival of Saturnalia. The Romans had it coming.
I'm celebrating CHRISTmas, not Soltice.
I will greet people with a Merry Christmas or a Happy Hanukkah. "Happy Solstice" is not part of my vocabulary.
The fact is, we celebrate the Holidays thanks to the Christian and Jewish tradition. If the end-of-years' celebrations were left as pagan winter festivals, the season would have died out with the Romans and the pagans.
If certain intolerant atheists don't like the Christmas or Hanukkah traditions, they are free not to celebrate them.