In Book X chapter 6 of the Ethics, Aristotle says “as different things seem valuable to boys and to men, so they should to bad men and to good”. This is a constant theme in the Ethics, found even in the first book. Aristotle sometimes gives another example, sc. that bad men are like sick men who can’t taste things as they are, and therefore perceive bad things as good and good things as bad. What objective standard could we invoke to establish something as sweet to both the healthy man and the sick man? This real lack of a common standard does involve a certain relativism between the good will and the evil will; the mature person and the immature person.
The experiences that reveal this kind of relativism are common. Maturity, or example, is best measured by the extent to which we become aware that what we once loved as the highest good, and which no one could talk us out of, is in fact less good or even wicked. Children don’t usually love most what is most lovable, and many of the things we burned to do in youth are things that we would be horrified at our own children doing in theirs.
Most attempts to reason with the wicked or immature are wastes of breath and often will only reinforce their convictions (try reasoning with a child). If you give a wicked or immature person a reason for why what they love is bad, they are more likely to judge your reason wrong in light of their loves than to judge their loves wrong in the light of your reason. Either they’ve never heard the reason before and so they will not trust it, or they’ve heard the reason before and so they’re sick of hearing it.
To the extent that moral relativism is the belief that reasoning does not reveal moral standards, and morality can only be the product of non-rational forces, there is a real moral relativism between the good and mature man and the wicked and immature one. The good and mature man can only reveal his reasons to those who are either like to him, or who love him. No one else can understand his reasons, and they can only be led by certain neutral forces that might be wielded either by good men or wicked ones: social pressure, art, music, the grandeur of law, the common practices of a people, enforcement of discipline etc.
It is horrifying to see that the will does have a real primacy and supremacy in the order of the good. There is a real sense in which reason is powerless against it. Will can be the source of that iron, omnipotent “no!” of a child, smugly denying anything.