Seeing the current "Keep Christ in Christmas" stuff makes me wonder about how Christians accepted Santa Claus. One could argue there is a connection between St. Nicholas and Santa, but the way Santa is described these days is its own legend and not something linked to Christianity. It seems like most people focus a lot more on Santa than on Jesus relating to Christmas, and they spend a lot more time, effort and energy on the gift giving related to Santa than on religious stuff.
This seems like something Christians should have objected to strongly a long time ago. Did many object strongly in the past, and how did those objections fade away?
Christmas in general has long been a holiday that Christians have objected to celebrating, especially among the Protestant religions. This is especially true after the Reformation.
In Early America and in England from the 1640s to early 1800s Christmas was actually a rather small holiday. This is primarily due to the influence of the Puritans and it is largely thanks to a change in opinion during the Victorian Era that has led to Christmas being celebrated the way it is today. We can particularly thank Charles Dickens and his A Christmas Carol along with the influence of Queen Victoria and Prince Albert for helping to popularize Christmas again.
Santa Claus on the other hand is also a rather new innovation. St. Nicholas lived from 270 to 343 and over time became an important Saint in Dutch areas. The Dutch referred to him as Sinterklaas.
The modern image of Santa Claus came about through the work of six different New Yorkers, ones with Dutch ancestors. John Pintard started to link Santa Claus to New York's history and Washington Irving even included the Saint in his publication, A History of New York, which was published in 1812.
The biggest impact though was the publication of the poem, Twas the Night Before Christmas. This poem was anonymously published in 1823 and has since grown to be perhaps the most famous poem ever written by an American. This poem is the first instance in which Santa Claus is depicted with reindeers and a flying sled.
Saint Nicolas' Feast Day is celebrated on December 6th of each year and due to the Advent season it was pretty easy to connect the him to Christmas.
As I mentioned, Christmas was not popular in early American society, but people did still celebrate two different holidays with various gift giving. Those two holidays were St. Nicholas Day and New Year's Day.
Once Christmas started to gain in popularity due to influence from Dickens, Victoria and changing opinions in general the merger of St. Nicholas with Christmas was also underway. This all happened in the course of the 1800s and gave birth to the Christmas holiday that we know today.
So to answer your question, the Christians who would have objected to Santa Claus already objected to Christmas. Those who were starting to celebrate Christmas for the first time decided to embrace Santa Claus. Many Christian groups still object to Christmas and/or Santa Claus, but Santa has become a part of Christmas for all the people who do not object.
Santa Claus is such a strong part of Christmas that he is even celebrated in countries like Japan where only two percent of the population are Christian and yet Christmas is pretty widely celebrated. Within the United States approximately approximately 73.7% of the population claim to be Christians yet approximately 97% of Americans buy Christmas presents.
So long story short is that Santa Claus is fairly new addition to Christmas and the objections to his addition have always been around. It is just that the holiday has grown far beyond just being a Christian holiday. Santa Claus is a piece of the secular side of the holiday and as long as Christmas continues to produce approximately 20% of the US Retail Sales each year Santa is not going anywhere.
Hopefully that helps. If you want anything elaborated please let me know.