Don't answer me as a Christian. Answer me as an atheist. Are you smart enough to figure out what utility value that our prior Christian framework provided? Are you sure? Or are you going to just start squealing about how Christ is an extension of the Egyptian Sungod mythology?
The problem with atheists (I know from direct experience) is that they are almost as crappy at atheism as most Krisschans are at practicing Christianity. Most all of these people don't even know what they don't know.
Behind every single successful civilization that you will ever learn of (as we progeny of Christendom adjudge success) there lies a simple unifying core ethical framework that any idiot can be taught in ten simple lessons. As a matter of fact, behind every single successful civilization there lies Christianity, period.
People won't admit it because they are creatures of vanity. The danger in admitting it for an atheist is the risk that they won't remain an atheist forever once they start to think about it.
I use to sit in Times Square in Wendy's Restaurant on a Saturday for many years in New York City and watch as my fellow secular humanists strayed in (habitually late, don't impose your values about timekeeping on me, man) and wonder if perhaps they might be the only group of people I had ever seen even sorrier than Christians. Once a man no longer believes in God, he will believe in most anything at all. Pity the society that needs to post one of these idjits on jury duty.