Claims of Christmas traditions being "pagan" are wildly overstated in popular media (it's certainly false to claim "most of the traditions" come from paganism).
Really? Which ones come directly from christianity?
Just as examples, the Roman festival of Saturnalia gave us many traditions, including decorating trees, exchanging presents, feasts, drinking and partying; the earliest version of Santa Claus can be traced back to Odin, who led a hunt through the sky, along with his 8-legged horse named Sleipnir. Kids would leave boots filled with carrots and straw for Sleipnir by their chimneys, and get presents in return. The yule log also comes from Norse tradition. Christmas carols can be traced back to the ancient Anglo-saxon tradition of wassailing (though the idea of singing songs during a celebration can be traced back to any number of pagan festivals). Mistletoe, and kissing under it, came from ancient Druid traditions. Also, it's said that if enemies met under mistletoe in the woods, they had to drop their weapons and declare a truce until the next day.
What unique traditions did christianity specifically add to the party?
One big repeated problem is that the argument essentially goes "look at this thing that pagans supposedly did, now look at this thing in modern Christmas celebrations, that shows copying" despite the fact that a whole lot of the time, the applicable Christmas traditions were only developed long after paganism in Europe had gone extinct (I've seen people try to say that Santa's reindeers come from paganism, despite the fact Santa's reindeer first show up in the 19th century).
See Sleipnir. Granted, a lot of the mythology surrounding Santa Claus came from similar legends and stories (including the Dutch Sinterklaas and St. Nicholas) and all got combined into the current legend we now know, mostly codified by Clement Moore, Thomas Nast and Coca-Cola.
To avoid accusations of Christian bias, here's an article by an atheist pointing out how a whole lot of supposed pagan connections in Christmas are incorrect:
Atheist activist Seth Andrews presents what he claims is the evidene that Christmas and its traditions are originally pagan. But his claims are nonsense.
historyforatheists.com
He's entitled to his opinion, of course, but the fact that traditions like saturnalia existed before christianity, and a lot of its specific characteristics became part of what we now call christmas shows the roots of the celebration.
But hey, I never said christians weren't welcome to the party. I just think it's pretty rude to declare themselves the host, and demand everyone else follow their rules, when they didn't start the celebration.
-- A2SG, but I still wish them a very happy holiday....however they choose to celebrate it....