It's always been a puzzle to me why religious people are granted so much authority in matters ethical. But a little thought makes it much clearer.
In the church in England, historically the leaders campaigned against literacy to prevent ordinary people being able to read the bible and decide for themselves what it meant. Mass literacy would undermine the status as experts of the clergy. Having the church representatives as the only people able to interpret what is declared to be the word of God enables the clergy to control the population's behaviour.
How is the control exercised? Through religious concepts such as sin, redemption, forgiveness. By inculcating these notions in the minds of a believing population, religious institutions can exercise control over the actions of large numbers of people.
Of course, one on one, the clergy would have a hard time maintaining this level of control. But when these customs and practices are embedded in social institutions, traditions, even laws, then people follow them as the natural way to behave. In that way, the church authority becomes something that represents the natural order of things. It becomes more unusual to contemplate differing from the teachings of the church than to question the irrational claims. When laced with notions of sin and damnation, the fear created is enough to suppress criticism. Of course, sometimes a burning stake was used to reinforce the belief.
When literacy is a means of power, because it is access to information, those who have that ability are seen as natural leaders of the social group. The priest, the monk, the Imam, is seen as the focal point of social power and their advice takes on an authority quite independent of the abilities of the person. They are both vehicle for a social message, and buffer against any divergence in behaviour from the religiously acceptable.
But what gives them authority in moral matters? Well, firstly they have access to authoritative scriptures, whether the Bible, Koran, or any other religious text. The social conditioning that puts authority in these texts, also allows the religious representative to inherit that authority.
Secondly, as judge of compliance with religious norms, the clerics wield very real power over the life chances of the individual - sometimes even the power of life and death. The religious state often uses force to compel religious observance. It is a dangerous business to oppose state-backed clericalism.
Thirdly, psychologically compliance to peer pressure provides social cohesion. To deviate from the state-sponsored religious norm is to put oneself outside of acceptable society and so some other mechanism of solidarity is needed before people will take the risk. If there are few dissenters, or if those who do dissent are persecuted, there are strong psychological pressures to conform, and rewards for those who do so.
Any expertise that religious clerics possess in ethical matters will come from a variety of sources. The social work done by vicars provides a source of social skills but not necessarily any particular expertise in ethics. Ethics is about the application of social values and where religious dogma is brought to bear, those values will be religious. Whatever the result of rational consideration, religious principles will predominate.
Therefore clerics involved in ethical issues are anything but objective and will have their rationality compromised by the need to promote their religious principles. For that reason, if for no other, religion should be kept away from children learning about ethical principles for without that separation, there is a significant risk of indoctrination.
So what might we expect from rational ethics? A consideration of the interests and well-being of those involved of course. Perhaps the application of some general principles such as the maximum good for the greatest number, with a proviso of protecting the interests of the minority. Any general ethics will necessarily come into conflict with religious dogma precisely because general ethical principles will be socially and historically determined - they change over time, and that conflicts with any ethics based on a dogma.
For that reason, many religions continue to reinterpret their religious texts to attempt to reduce the conflict and maintain their social influence. Those religions which defend the letter of the text, such as Islam, have a particular problem in this respect. The religious teachings become increasingly anachronistic, and their defence more vigorous and dictatorial.
