Why do atheist's care to get so involved in religion?

I'm an atheist and when I see that the atheist group or whatever have gotten rid of crosses representing deceased troopers, I can't understand why. As an atheist I don't care if there are crosses, or in god we trust on our money. I don't believe in god but i'm glad some people do because the bible teaches good ethical practices. And if you can't just be a good person because it's the right thing to do, and a bible helps you, good for you. But I don't want to push my non-belief on people or stop other people from having their beliefs. This is why people think were arrogant a holes.