"If they hear the word of God and are offended, who is biased then?"
Both Christians and non-Christians. Don't go saying you aren't biased. You're suggesting we throw out a Constitution that's very existence marks an attempt at order and peace in a nation of diverse cultures. What right do you have to throw it all away for the selfish desire of mass conformation to an ideal that only a fraction of the world carries?
As for common sense, of course that makes sense, but again, you haven't answered the fact that you can't force a nation of diversity to believe what you believe in. The first 4 commandments are, by far, the most ridiculous to an atheist. I'm Christian, and even I see the flaws of it.
Next, how the heck do you think the nation would support itself? 'Thou shalt not kill' says goodbye to the national military. 'Thou shalt not bear false witness of your neighbor'. Name me one human who has never lied in his life. Even you are guilty of lying at some point. If you'd never lied, you'd be 1 out of 7 billion, so the odds are against you.
You think some moral guidelines are enough to keep 300 million people happy? Fat chance. Your narrowminded idealistic views of right and wrong is misguided. For, no matter how righteous your intention, you can't apply that to a government. It eventually degrades into nothingness and anarchy, or worse, an autocracy. If you'd ever taken a Government class (I have, very recently in fact), then you'd know that 10 simple rules about how to be a good person won't keep a nation intact. Open your eyes to the conditions of the world, not just the conditions of your moral ego.