@Timboslice also Jesus was likely born in Nazareth, not Bethlehem. But there is documented tradition that Christians were celebrating the birth of Jesus in Bethlehem on Dec 25th as early as 300AD. Not related to any existing pagan festival.
The date is likely to make it so he was conceived on Easter. But could also be historical accurate. Who knows. Doesn't matter. If the earliest Christians weren't having these fedora wearing arguments it's good enough for me.