Peter Singer‘s essay “Moral Experts” [1, pp.3–6] in Writings on An Ethical Life  originally appeared in Analysis, volume 32, pages 115–117, 1972. It is an attempt to respond to the statement that moral philosophers are not moral experts. A reason accounting for this view is that the role of a moral philosopher is different from that of a preacher. Another reason explains that moral judgements are purely emotive, that a person’s moral view is as good as anyone else’s (ethical relativism). Both of these reasons, Singer maintains, are lacking to some extent.
According to Singer [1, pp.3–6], a more plausible reason is that knowing the difference between right and wrong requires that we care about the issue at hand. It is not enough that we know; we also need to invest time and energy into investigating the moral fabric of an issue. A society whose moral code is perfect and undisputed obviates the need for a morally good person to reflect on the moral principles of that society. But in the absence of such a society, we need to decide for ourselves what we ought to do. This is an onerous task that requires substantial investment of time that we might not have.
A moral philosopher has several advantages over an ordinary person. First, the former’s training in philosophy equips her with skills in argument and detection of invalid inferences. Second, the experience of the moral philosopher enables her to understand moral concepts and the logic of moral arguments. Third, a moral philosopher has the advantage of being able to devote full-time to reflection on normative issues.
 P. Singer. Writings on An Ethical Life. Ecco, 2001.