Moral false-positives (failing to recognize an unethical behavior as unethical) are probably more costly than false-negatives (failing to recognize an ethical behavior as ethical). But moral false-negatives are costly, too.
Hugh Ristik, LessWrong (February 8, 2011),
Where almost everyone feels that a particular kind of conduct is wrong, that might seem solid evidence that such conduct really is wrong. But Mill is not denying that our moral feelings provide some prima facie support for our moral opinions. If we feel that torturing children or stealing bread from the starving are wrong actions, then they probably are wrong. However, it is worth remembering some of the other moral feelings that people have also had in the past. Thus at various times people have felt that it was right to burn heretics and witches, to practice slavery, to expose unwanted children, and to punish severely wives who were disobedient to their husbands. Reflection on such cases supports Mill’s contention that feeling is an unreliable guide to moral truth, and that it is dangerous to treat it as a final court of appeal. Following Bentham, Mill demands that our moral opinions should be answerable to some external standard—that is, that we should be able to articulate reasons for them that go beyond a statement of our gut feelings, attitudes or ‘intuitions’. The provision of reasons for moral beliefs makes moral debate possible, from which truth and enlightenment can emerge. By contrast, dogmatically insisting that one already knows all the moral answers via one’s feelings or intuitions forecloses the possibility of an escape from error should those feelings or intuitions be wrong. Mill’s position is therefore better described as one of moral caution than of moral skepticism. His aim is not to persuade us that moral knowledge is unattainable, but to warn us against supposing that it can be securely attained by a purely subjective process unassisted by reason.
Geoffrey Scarre, Mill’s On Liberty, London, 2007, p. 99
[A] feeling of liking or aversion to an action, confined to an individual, would have no chance of being accepted as a reason. The appeal is always to something which is assumed to belong to all mankind. But it is not of much consequence whether the feeling which is set up as its own standard is the feling of an individual human being, or of a multitude. A feeling is not proved to be right, and exempted from the necessity of justifying itself, because the writer or speaker is not only conscious of it in himself, but expects to find in other people, because instead of saying “I,” he says “you and I.”
John Stuart Mill, ‘Whewell on Moral Philosophy’, in The Collected Works of John Stuart Mill, Toronto, 1988, vol. 10, pp. 178-179
When I am in pain, it is plain, as plain as anything is, that what I am experiencing is bad.
Guy Kahane, The Sovereignty of Suffering: Reflections on Pain’s Badness, D.Phil. thesis, University of Oxford, 2004, p. 2