Actually, you can tell someone what to do on the basis of it being “wrong” or “right”; the only requirement is that their morality/preferences are similar to your own. If you can convince them that their actions are contrary to their own moral preferences, you could manage to convince them to do that which you both consider to be “right”.
But, if you meant that it is impossible to determine what someone should do by means of a universal set of moral rules, then yea, clearly not. But the absence of a universal morality does not imply an absence of all morality.
Actually, you can tell someone what to do on the basis of it being “wrong” or “right”; the only requirement is that their morality/preferences are similar to your own. If you can convince them that their actions are contrary to their own moral preferences, you could manage to convince them to do that which you both consider to be “right”.
But, if you meant that it is impossible to determine what someone should do by means of a universal set of moral rules, then yea, clearly not. But the absence of a universal morality does not imply an absence of all morality.