Do atheists even need an objective moral system?

[Whateverist]

TO THE OP: No, no thank you. We will hash out the rules we'll live by and then hold each other accountable based on our own sense of fairness. That'll get it done. Feeling smug and superior in an ultimate way isn't necessary. We can negotiate the degree to which we will supress our impulses out of consideration of others, codify what we find necessary and leave the rest to good manners.