Those who engage in combat to remind others of "the reason for the season" would do well to remember that the Christmas season as such has only existed for about a century and a half. The 1,500-year-old Christian season that precedes December 25 is Advent, a time of fasting, penitence, and somber waiting. Protestants who eschew Advent because of an association with Rome have precedent for doing so. But the Reformers, Puritans, colonial Baptists, and others who gave rise to modern evangelicalism either passed Christmas Day with a simple worship service, or strongly opposed such a "popish" observance.
But please, the next time you're in Wal-Mart and the clerk wishes you "Merry Christmas," don't get an angry look in your eye, poke your finger into the clerk's chest, and say, "It's Advent! Christmas isn't until December 25!" That would be really annoying.
Source: Christianity Today
It should be noted that Christianity Today is an evangelical publication, but even here people are getting tired of all hype which some evangelicals are manufacturing about the so-called "Christmas Wars." A poll is cited showing that only 28% think that there is some improvement behind forcing stores (under threats of boycott and public protest) to say "Merry Christmas" instead of "Happy Holidays."
At the same time, though, we aren't hearing so much anymore from Christians about the problem of Christmas being overly commercialized. Christians used to lament this, but not so much anymore. I guess that goes hand-in-hand with Christians now treating the Christmas season as a time for feasting, parties, and sensual delights rather than fasting, penitence, and somber reflection.
Some atheists don't celebrate any holidays at this time of year, but those who do celebrate a variety: Christmas, Solstice, Hanukkah, etc. For atheists, as with most of the rest of the non-Christian population, "Happy Holidays" is the most appropriate greeting. It's also appropriate for Christians because few of them only celebrate Christmas. There is New Year's, after all.
The phrase "Happy Holidays" is the most inclusive one possible -- which may be why it's such a problem. Some Christians don't want to be "inclusive" because that sends the message that they aren't special or deserving of special privileges. Being inclusive means treating others as full equals, deserving all the same dignity and respect as oneself. The fact that this is received as an insult by some Christians says a great deal about them as human beings.