The (heavily cited!) Wikipedia article says this
Following the Protestant Reformation, groups such as the Puritans strongly condemned the celebration of Christmas, considering it a Catholic invention and the "trappings of popery" or the "rags of the Beast."...Following the Parliamentarian victory over Charles I during the English Civil War, England's Puritan rulers banned Christmas in 1647...In Colonial America, the Puritans of New England shared radical Protestant disapproval of Christmas. Celebration was outlawed in Boston from 1659 to 1681. The ban by the Pilgrims was revoked in 1681 by English governor Sir Edmund Andros, however it was not until the mid-19th century that celebrating Christmas became fashionable in the Boston region...Christmas fell out of favor in the United States after the American Revolution, when it was considered an English custom.Washington Irving wrote short stories about Christmas, and that made it fashionable again. The wikipedia article addresses that, too.
What I've gathered, as well, is that the people who want to KEEP CHRIST in CHRISTmas don't actually care about religious celebration, other than not wanting to feel dominated or ignored...and they prefer to dominate others. (I'm not talking about everyone, but the most vocal people.) I tweeted a few weeks ago that for there to be a war on Christmas happening, the music at Starbucks was awful Jesusy. The religious celebration they want to do isn't so much celebrating, as maybe remembering that Jesus was born. That's great, do some remembering.
But I think that another way of maintaining Christmas as a religious holiday is to celebrate it with religion. When I've tweeted something to the effect of keeping Mass in Christmas, I've gotten the response (and I'm not the only one) to get "Isn't keeping Christ in Christmas more important?" Well, like I said above, I haven't actually noticed an absence of Christ....and if you celebrate Mass (or some other communal celebration of the holiday, gathering around Word and preferably Sacrament) it's hard to not have Christ in Christmas. And I'm willing to have a pretty vague and generous definition of mass, namely a gathering of the religious faithful, regardless of their tradition, to celebrate a feast day.
Thom, SFO offers the following about keeping Christ in Christmas:
Instead of inaugurating the Christmas season at Thanksgiving or Halloween, try living the mysteries of Advent. Try preparing yourself for the coming of our lowly king. Try not spending 6 months salary on gifts to impress friends, family, co-workers, and neighbors. Instead, take that money and do some real good. Try tempering the joy of the season with the stark reality that we are still in darkness.I like it. To it I'd add not just waiting until Christmas to celebrate, but also keeping all of Christmastide. Twelve days instead of one is a lot more celebration! I've also heard people say (often in response to the statement "It's only Advent!") "It's never the wrong time to celebrate Christ's birth." Well...maybe. As TBE says, you wouldn't sing "Jesus Christ is Risen Today" on Good Friday...and you don't say "Merry Christmas!" in July. I don't think Christ is really absent from Christmas, not even in secular settings; certainly not absent if Christians actually celebrate (especially together) the mysteries of the Incarnation (which is not celebrating Jesus being born to die; cf John 1....and I don't think singing "Happy Birthday" to Jesus is quite it, either).
If we keep the Mass in Christmass, Christ will surely follow.