At http://www.uncg.edu/~nphuntbu/lectures.html (site now discontinued), I found a set of lecture notes entitled “Why religion is irrelevant to ethics”. Here is a quotation I particularly liked:
Why are members of the clergy (who presumably are experts in the theology of their particular sect) assumed to be experts in ethics? Why put them on ethics ommissions rather than taxi drivers or literature professors?
This issue obviously boils down to presuppositions. If you assume a priori that a member of the clergy is an expert on ethics, the above questions will be a non-starter. If, however, your mind is open to the idea that just because someone is a member of the clergy, they are not automatically qualified to be an expert on ethics, then this question will be more interesting to you.