The problem is that society and the people around us gravitate towards what is popular rather than moral or ethical. The structure of our society was based on ideas pulled from Jewish and Christian traditions. The 10 commandments, the family as the basic unit of government, the idea that you don’t regulate something nationally that can be done at the state, local, or family level. Capitalism is a natural progression of this. Capitalism is really just the idea that two people should be able to enter into an agreement without interference from a third party.
The problem with a secular society choosing morality is that it is corrupted from many directions. Some fall to the fallacy of pure logic, like the bioethics crowd. They have missed the basic truth that it is wrong to commit murder. The hedonists Argue that there is no true right and wrong.
A religious basis is not immune by any stretch. I don’t remember manifest destiny in the Bible, but we kicked the Indians out anyways. Some hardcore Christians hate gay people. Or black people. Or white people. Etc. these are all failures to follow the principles of the Bible. But a religious base gives us a moral compass to steer back to when we do. “Hey, maybe slavery isn’t the best idea”. “Hey, maybe we should be more tolerant of the Irish, or the Germans, the Chinese, etc, etc”. A secular basis for morality doesn’t provide that kind of moral compass.