“Atheists can’t be trusted to operate morally,” basically means “If I weren’t being threatened by eternal damnation I’d be a complete bag of dicks, and I can’t imagine anyone else doing better than me at self-control, either.”
When we agree on the same religion, we are agreeing simply to paint our doors all the same color to impress our neighbors.
This has no connection whatsoever with the contents of the building itself. A person can claim any religion they want and act any way they like — a successful religion includes conditions under which this is inexplicably okay.