Maybe we're missing a simple fact here.
The ten commandments (like the cross, the star of david and many other images) have become merely a symbol, a touchstone that is used by many to remind themselves to just "be good".
Like you, i am an atheist and, as such, am constantly amazed by the blind faith of the masses and their unwavering devotion to such a primitive mythology, but do their symbols truly harm anyone.
Of course, most believers don't objectively study their idols (why would a christian revere the implement of his god"s physical destruction), but what harm is there in placing these symbols in places where "believers" can be reassured by them.
Like it or not we live in a "christian" society and their symbolism surrounds us every day. They once were in a minority position (more desperate than our own) and endured, let us be a bit more gracious than their violent history shows them to have been.