The Date of Christmas
This kind of dating issue isn't something that has ever interested me either as a historian or as a Christian. However, without knowing anything about how it fits into scholarly discussion of the topic, I find this thesis interesting. The most common explanation, that December 25 was chosen to distract people from some festival around the time of the Winter Solstice, does fit practices of theological co-option common in the history of most religions. The fact it is weak at the level of finding the human agents and explaining their mindsets is probably not enough to undo it given my impression of the source material.
Evidence suggests, however, that Christians commemorated Christmas in December during the 3rd century, and perhaps even earlier. It was around 200 that Christians calculated a March 25 date for Good Friday. McGowan's earliest source for the connection between Jesus's conception and crucifixion, however, is from the 4th century, so I'm not sure it follows that calculating the date of the conception came first and led to the birth. That said, as liturgical dates seem to have come from calculation and those are the earliest calculations we have, I can definitely see it. This, in turn, let's us see a much more subtle form of religious influence, for once the date is in the calendar, it perhaps begs to become a Christian version of other late Roman winter celebrations, much like Hanukkah, though a lesser holiday within Judaism for centuries, has become a "Jewish Christmas" in majority-Christian societies.