OK knowing my reputation for cynicism let me preface this post with the promise that the question I ask and the reasoning I use to come up with the question are genuine and not meant to derail, demean or in any other way devalue this thread.
Question: Why would I care what Jesus' birthday was?
Unless I was a Pharisee of the times perhaps and watching over the young lad to make sure he got his Bar Mitzvah on time, or some such other calendar driven event, his birth would seem to be pale in the face of his sacrifice and resurrection.
The birth was simply an entrance into the world - an unpleasant place at best; little noticed by contemporaries at that; and not noticed by the local powers (Rome & Jerusalem).
The death and resurrection was the culmination of Jesus' public and indisputable victory over evil and the promise to all mankind of their ultimate victory as well. Now those dates - heck yeah - those are worth remembering regularly. Hey Martha!!! Tomorrow we can party and celebrate how Jesus kicked Satan's azz right into the 16th sub-basement of the heavenly outhouses. Make sure you pick up some tequila and limes on the way home from work! Ohhh - I'm a month early?!?! So what let's celebrate the victory anyway!
Further, if I am going to watch dates, verify actual dates through several calendar changes etc, I got bad news for those congregational types. I am really going to celebrate Jesus' victory with some margueritas and some grilled steaks. No need for putting on a suit and tie and sitting in an uncomfortable chair while someone intones the same snot as last year. Let's party over his victory. Steaks this year! Seafood next year. None of that repetitive congregational snot.