The many letters addressed to Christians which implore them to keep Christ in Christmas is just a reminder that physiological truth does not have to be based in fact. In these cases absolute certainty is usually a far cry from truth.
The fact is that Christians had started to incorporate pagan rituals into their customs and traditions which over time was absorbed into their culture. The truth is that Christmas, Halloween and Easter are basically the same. After much effort of cleansing failed to remove the pagan scourge the next best option was to hijack their calibration adopting them as their own. This is why I have come to the conclusion that the phrase that Jesus is the reason is obnoxious and Ignorant.
Solstice holidays are generally celebrated across the world more so in the Christian religion. There are even instances where its secularity is present in nature. In such cases you need not have to believe in the fertility god Yule to be apart of the Yuletide merrymaking nor do you have to be Wiccan to jingle bells or a Druid to deck the halls with holly, you need not believe in Thor son of Odin or Santa Clause to enjoy giving gifts at Christmas or Saturn to put up a beautiful Christmas tree. And finally you do not have to believe in the Mithras faith to celebrate the rebirth of the sun on the 25th of December.