This is probably a major reasons why religious people distrust atheist religion can be looked at as a moral consensus. It is a system of rules which it's adherents (sometimes nominally) agree to live by. By declaring themselves atheists individuals choose to publicly reject that consensus which leads to suspicion. The bitcoin equivalent would be a miner publicly supporting a closed source hardfork.
That Scientific American article describes that as un unsupported cognitive bias. Just because people distrust atheists doesn't mean there's a reason for it.
And just because many religious people feel they need religious rules in order to act morally it doesn't mean that people who don't follow religious rules can't act morally. It's more likely that religious people need religion in order to be moral actors, just as BADecker wrote.
Anybody can act anything by accident. Give a monkey a typewriter, and he is bound to type a word sometime.
All moral laws that atheists follow spontaneously come from the writing of the laws that God did in their hearts. When the time comes that we actually understand the genome completely, we will find the moral laws written right in the genes.
