Before christianity, this time of year celebrated the "births" of many other religous icons like Mithra, Horus, Thor, Dionysus, Helios, ect. This is so prevalent because these few days are when the days become noticeably longer, which many cultures associate with birth.
Even if Jesus ever existed, no one knows his true date of birth. However we do know he wasnt the only one people believed to be born of a virgin. Others include Krishna, Bacchus, Yu, Hercules, and Zunis, who was eventually crucified.
So in order to acknowledge christianity and all these other religions, I wish you all a Merry Mythmas!
So forget about religions, throw that imaginary bullshit out the window. Enjoy what you've got and spend this finite existence we each have with the people you care about.