Christmas usurped the pagan feast of Saturnalia, absorbing several of its symbols. That doesn't seem to bother you. Why the double standard?
This is a pretty common meme, but it's not exactly what one might call true.
The Saturnalia was a multi-day time of feasting, the number of days differed depending on the time (Roman emperors had the authority to add or subtract days). At its shortest it was a five day period of feasting, but generally it lasted for about seven days, from December 17th to December 23rd. It was celebrated by feasting, drinking, the exchanging of gifts, and household role reversal--masters would take on the role of servants, while slaves and servants would be then served by their masters.
With the general Christianization of the Roman Empire in the 4th and 5th centuries, the Saturnalia largely only survived as a cultural relic, its religious significance declined. It wasn't replaced with Christmas, it simply faded into non-observance. By the fall of Rome in the West in the 5th century, it was called the "feast of the slaves" and was simply a time for masters to give their slaves and servants gifts. This also faded in time.
Gift-giving was not associated with the Feast of Christmas in Christianity at this time in history. Though gift exchange may have survived as a general "thing to do" in the winter season.
In many parts of Western Europe the big gift-giving day in winter became the Feast Day of St. Nicholas (December 6th), and it is specifically these St. Nicholas Day observances that, in the 19th and 20th centuries, were slowly transferred over to the popular celebration of Christmas in the English-speaking world, and then the influence of the English-speaking world to elsewhere. The Dutch custom of children leaving their shoes outside the front door on the eve of St. Nicholas Day for St. Nicholas to come and leave money in their shoes evolved into the well-known custom of hanging stockings on the chimney on Christmas Eve--through the Dutch influences that remained in New England (New Amsterdam --> New York).
For most of Christian history there simply haven't been that many customs associated with Christmas. It was a relatively minor Christian feast day compared to the bigger times of the year: the Paschal Feast (Easter), Epiphany, Lent. About the most that could really be said is that people tended to like to drink on Christmas. It's really only been in the past several centuries that we begin seeing most of the things we today associate with Christmas, Santa Claus (St. Nicholas, one of the St. Nicholas Day things that came to be associated with Christmas), the exchanging of gifts, hanging stockings, etc.
The origins of Christmas itself are largely tied to the ongoing discussions early Christians were having about when Jesus was born. These conversations were largely happening in the 3rd century, and there were several popular theories. Two of the biggest were built upon the idea that since Jesus was perfect, He must have had a perfect life--meaning that He died on the same day He was either conceived or born. It was pretty well agreed at the time that Jesus had been crucified on a March 25th, and thus those who argued that He was born on the same day He died, argued that He was also born on March 25th. Those who argued that Jesus was conceived on the same day He died, argued that He was conceived on March 25th, and then added nine months for His birth, which just so happens to be December 25th. In other parts of the Church the birth of Christ was simply being observed as part of the already established Christian feast of the Epiphany (January 6th), which is why even to this day the Armenian Apostolic Church (the historic Church in Armenia) celebrates Christmas on January 6th, not December 25th.
There really wasn't a standardization of when to celebrate the feast of Christ's birth for some time, eventually most ancient jurisdictions adopted December 25th as the feast of Christ's birth, but as mentioned already, this wasn't universally the case as can be seen with the Armenian Church. It can be easy to imagine that the Christian Church in antiquity simply engaged in fiat decision making on something like this, but that's not really the case. In antiquity bishops held semi-autonomy, that is there was no "pope" in the modern sense to make decisions that all the other bishops had to accept. And so practices could vary from region to region. This is why we don't see a standardization of how to calculate the Paschal Feast until the Council of Nicea in 325, which chose the most common way churches all over the Christian world were already calculating when to celebrate it. Even still today, the highest ecclesiastical authority among the Eastern Churches is the church council--a coming together of bishops to reach a consensus. It is only in the West, with the evolution of the papacy, and the defeat of Conciliarism in the 14th century to consolidate papal authority following the Papal Schism that the idea of a singular central church authority truly arises in Christendom.
Which is all just to say that the origins and history of Christmas, in the popular consciousness, isn't historically and academically sound--these are ideas that gained popularity in the past and so they never really went away, but today we generally can agree that there just isn't anything to substantiate. Even the most academically sound conjecture--that December 25th grew as the popular day to celebrate Christmas in order to combat the pagan feast of the Dies Natalis Sol Invicti (Birthday of the Unconquered Sun)--is only that, conjecture. The earliest mention of the Dies Natalis is from the mid 4th century (354 AD specifically).
-CryptoLutheran
