What would christmas look like if the many angry christians were successful in de-secularizing the holiday? Really, it would look like one of two things.
Christmas might become a fringe holiday, celebrated in churches and the homes of the "christian faithful." It might be a holiday that we heard very little about anymore. Perhaps December 25th would be renamed as a secular federal holiday; say, the Day of Giving or something equally universal and unoffensive (although some religious nut somewhere would be offended). We would no longer hear christmas carols, except on christian radio and in christian stores; instead we would hear holiday songs. We would have our holiday trees and lights and decorations and food and presents. The nativities and creches might have their own separate aisle for the "christmas celebrators" (similar to how Hanukkah merchandise is relegated to one aisle separate from the rest of the holiday stock). Perhaps the christmas celebrators would go back to the old christian tradition of viewing the decoration with trees and lights as pagan, and we could have an easy dividing line between those celebrating christmas and those celebrating the secular winter holiday.
But that's not really what christians are going for when they fight secularization of the christmas holiday. Nope. And I think we all know what they are going for. There's only one good word to describe it; theocracy. A country where everyone who celebrates the holiday must do so with acceptance of the presence of baby Jesus as the reason for the season (even if it's just implicit acceptance by not raising a fuss when courthouses and congress buildings put up nativities and trees with angels at the top). A country were people pretend for at least a day that they have no complaints against christianity, that they accept and appreciate it. A country where no one celebrates a christmas that's conspicuously devoid of Jesus/god/biblical decorations, songs, and other reminders. In other words, a monotheistic country. "Sure," they may say, "you can celebrate your separate religions instead." Well, for now maybe. But come on, claiming a monopoly on an entire holiday season, and then claiming that they are willing to share it as long as people make sure to differentiate? That seems like the kind of concession that would only last for as long as it had to. If atheists, agnostics, humanists, and other non-believers in a particular religious faith all left christmas alone or celebrated it in a "christian way" do we really believe that Hanukkah or Kwanza or some other holiday wouldn't be the next target? If christians cannot live in harmony with those who don't believe, why would they be able to live in harmony with those that don't believe rightly?
Which is why, regardless of my personal beliefs about christmas, I am willing to fight for the right to leave baby Jesus and his manger out of christmas, to celebrate without carols or midnight masses, to be joyous and make merry without a maker to thank, to give gifts to each other out of love for humanity and not a deity. After all, there is no religious freedom if unbelief, disbelief, skepticism, doubt, and rejection aren't options too.