Ten Commandment displays

I am confused and would love for someone to explain to me why there is so much controversy over the ten commandments being posted in public places. Is it just because they appear in the Bible? Because to me it is a great set of rules for everyone to follow. Just think what a better place this world would be if everyone would live by those rules. I don't think it should matter where they originated as much as what it means for society to co-exist.