Should religious leaders be banned for providing moral viewpoints in public policy? Absolutely!
It is completely wrong to assume that religious leaders have any higher moral standards than you and me. For public policy decision, religious groups may be viewed as another lobby group trying to further their interest. But in no way should they be consulted as a moral leader.
Here are my reasoning.
God does not exist. (Prove to me otherwise and I am happy to convert).
Religious leaders who really believe that god exists are clearly delusional or lack the ability to make reasonable conclusion. How can we judge their input in anything, including moral arguments.
Religious leaders who know that god does not exist but continue to insist the false doctrine are lying to themselves and the followers day in day out. How can we trust them, morally in particular?
It is well known that religions have been a hinder to progress of science. Let's not let them hinder the progress of human moral.