I really hate all this stuff because it forces me to defend something that I don't really want to defend. The bottom line is that if we are to take the First Amendment seriously, then the government is to take absolutely no part in establishing a religion of any kind. If public property is going to be used to endorse one religious belief over another, then that's going against the Constitution. And you can hem and haw all you want; a manger scene is a religious symbol of Christianity. Nobody's confused and thinking that it's Vishnu in that manger. It's an image that's steeped in Christmas tradition. If even one non-Christian is offended by it or feels its inappropriate, then the government has no business letting it be up there.
In other words, the atheist groups are right.
However (and you saw this coming)...
I would like to plead with my fellow non-Christians by saying that there's no reason that a manger scene should offend you. Yes, it is a religious symbol. Yes, it doesn't technically belong on public property. But ya know something - if you live in California, then you should also protest all state government buildings that feature the official seal of the State of California. Why? Because it's got Minerva, the Roman goddess of war and wisdom on it. And while it's true that you're pretty hard-pressed to find people who still believe in her and worship her, it's just as much of a religious symbol as any manger scene.
Now, before you go out wasting time and resources on protesting the seal of California, think about how much that actually offends you that it's there. Well, that's how much a manger should offend you. Whether you like it or not, we do live in a country where Christianity is a major aspect of the culture. Manger scenes reflect that. Sure, it doesn't represent EVERYBODY's culture, but unless we start getting a major segment of society that's not Christian, then we'll start thinking about statues of Krishna. (And honestly, I wouldn't mind statues of him in the public square come the next Diwali.)
As atheists, we don't really have an equivalent. I mean, do any atheists really feel anything deeply transcendent when they see an image of the Flying Spaghetti Monster? Yeah, I like him too, and I even have an FSM decal on my car, but come on, it's not the same thing. And no, a statue of Darwin wouldn't do it for me either. I like what the man has done for science, but I admire the science more than I admire the man. His knowledge wasn't revealed from a higher power, and somebody else would have figured it out if he hadn't.
Maybe this is why these atheists groups are doing this. I guess it's easy to feel left out. But surely I can't be the only one who thinks that a manger scenes are nice, right? Shoot, if I had a lawn and somebody gave me one, I just might put one out myself. A baby is born and people come to see. That's a nice sentiment. Yeah, I don't buy into all the details of the story, but the thing is with symbols is that they can mean anything you want them to mean. For me, it reminds me of life when all around things are dying off (literally - the leaves on the trees and figuratively - the sun). Now, if the manger scene was accompanied by a message that said something like: "Don't believe He's the son of God? Hope you like HELL!!!" then we'd have something else to talk about. Also, I don't think that I'd care much for a cross, and I think that I'd actually get out and protest myself if it was a cross with an image of the suffering Jesus on it. Something about public torture/execution in a public square just doesn't seem appropriate to me, and I don't care how believers interpret it.
Non-Christians, and atheists in particular, need to pick their battles more carefully. Considering that there are so many people out there who don't trust us and think that we're immoral by nature, our first priority is just letting people know - in a positive way - that we're out there. We're their friends, their neighbors, their co-workers, and we'll only eat their babies if the babies look REALLY tasty. All this chickenshit stuff just serves to upset people. What's worse, it gives the Bill O'Reilly types and various fundamentalists fuel for their fire so they can act like they're being oppressed. The way you hear it, you'd think that atheists were making people take Christmas trees down in their own homes.
Quit helping their cause. When atheists are given the respect they deserve throughout the country, then you won't give a crap about a manger one way or another. It'll be like what the average Egyptian no doubt thinks of the pyramids. Yeah, it's a religious symbol of a belief system that's not your own, but it's not coercing you into believing anything.