... to argue that moral judgements can be rationally defensible, true or false, that there are rational procedural tests for identifying morally impermissible actions, or that moral values exist independently of the feeling-states of individuals at particular times.
... if we adopt the principle of universality : if an action is right (or wrong) for others, it is right (or wrong) for us. Those who do not rise to the minimal moral level of applying to themselves the standards they apply to others -- more stringent ones, in fact -- plainly cannot be taken seriously when they speak of appropriateness of response; or of right and wrong, good and evil.
In fact, one of the, maybe the most, elementary of moral principles is that of universality, that is, If something's right for me, it's right for you; if it's wrong for you, it's wrong for me. Any moral code that is even worth looking at has that at its core somehow.
The source or justification of a universal ethic may be thought to be, for instance, human nature, shared vulnerability to suffering, the demands of universal reason, what is common among existing moral codes, or the common mandates of religion (although it can be said that the latter is not in fact moral universalism because it may distinguish between gods and mortals). As such, models of moral universalism may be atheistic or agnostic, deistic (in the case of several Enlightenment philosophers), monotheistic (in the case of the Abrahamic religions), or polytheistic (in the case of Hinduism). Various systems of moral universalism may differ in various ways on the meta-ethical question of the nature of the morality, as well as in their substantial normative content, but all agree on its universality.