One of the puzzling features of undergraduate moral relativism is that students seem to think that their moral relativism in some way either supports or is required by a notion of tolerance for other people's practices and beliefs. This is puzzling because, after all, if relativism is true, then if I believe or society believes (depending on whether the relativism is individual or social) that someone's variant practices and beliefs should be squelched and the person should be punished for them, then this is the right thing for me or for society to do. In fact, this consideration is a good reason to abandon relativism.
Still, it is a good question why it is that students hold together the doctrines that (a) moral relativism is true, and (b) moral relativism connected with tolerance. Do we just want to say that they are massively irrational[note 1], or that this is just an effect of original sin, or is there a more proximate and specific explanation?
I want to offer two different hypotheses. The first hypothesis is that students confuse together the concepts of culpability and wrongness. A person may do wrong, but not be culpable for it if she does not know that what she is doing is wrong and she is not culpable for this ignorance. Conversely, a person may do the right thing, under at least one description, but still be culpable, if she erroneously believes it to be wrong. A certain tolerance goes together with considerations of inculpability. If someone is engaging in some immoral activity but doing so inculpably, then it makes sense to be tolerant, provided that undue harm to society does not result. From the claim that the Nazis believed what they did was right, the relativist laboring under a confusion between culpability and wrongness concludes that what the Nazis did was not wrong (for them). However, interestingly, in one's own case, what one believes to be wrong and what is culpable come very close (there is still a gap since one can do what oen believes to be wrong but be non-culpable on grounds of internal or external compulsion), and hence the confusion does not significantly affect a lot of first-person deliberative behavior. Thus, a typical individual relativist still tries to figure out what is the right thing to do, and consults with others, even though this makes no sense given that whatever she believes to be right is guaranteed to be right.
The second hypothesis is different. Consider first a relativism about an area of life that does not expressly involve ethics, say esthetic or gustatory relativism (what is beautiful or tasty to me may not be beautiful or tasty to you, and there is no objective, mind-independent beauty or tastiness). This kind of relativism does support quite a bit of tolerance. If Century Sundae is not tasty to you in the way it is to me, I should not impose it on you, and I should be tolerant of your desire to eat the mildly repellent (to me) Chunky Monkey. Here, the relativism is sufficiently limited that it does not undercut, but instead supports, tolerance.
As a result of this, one might conclude that relativism in general supports tolerance about the praxis that is relatively evaluated. However, in the special case where the relativism is moral relativism, this does not hold. The reason that esthetic or gustatory relativism supports tolerance is because of objective moral principles concerning respect for differing preferences and views. But once the relativism becomes moral relativism, these principles are undercut, a fact one might easily miss.
Or maybe they are not entirely undercut. After all, if one is a "nice" person who believes that one should be tolerant of people with differing practices, then individual relativism renders this belief self-justifying. But of course individual relativism would equally render the opposite belief self-justifying.