> but it is funny how up until the 1950s christmas was deemed a pagan religious holiday and was even listed this way in encyclopedias from that time

Deemed by whom and in what encyclopedias? There are certainly religious groups who are historically recent offshoots of Western Christianity that viewed it that way in the 1950s, but the same groups do so today, nothing substantial has changed on that front since the 1950s. For the rest of Christianity, well, it was adopted as a Christian feast in the 4th century and has been treated as one since pretty consistently by most of Christianity. Certainly so in the largest branches of Christian in the US in the 1950s, which constituted between them the great majority of the population.

I had a copy of Britannica from the 50s that had this. It was picked up in one of those Books By The Yard for cheap.