As a humble POV is scarier than the most blunt fanaticism, relativists are received as dangerous rebels. But deep down they do not present an opposition to realism, they are only humble about assumptions.
Realists say “Humans can understand the world around them”. Relativists reply “Well… maybe. Who knows? That is an assumption, though, and we have no idea whatsoever about how to confirm such a bold claim.”
Both are pretty decent epistemological frameworks. Neither is right. The second has the decency of admitting its own absence of certainty, the first has this naïve and always laudable want to go on despite evidence to the contrary. As a system for understanding, a cautious, parsimonious, and impartial mix of both is bound to be more powerful, but there is a problem in this alliance.
And it is this: Realists have a basal fear of Relativists. It is not like they have a reason to dislike relativism, they have a primal attitude that forces them to fight and hate relativism at all costs.
While meekness seems to be the weaker attitude, the not-aggressive one, intellectual humbleness is something of a completely different ilk. The Humble Point Of View (HPOV, for short) is more in line with Selective Aggression — but the correlation here is excessively subtle!
HPOV means you change your mind. You are not certain of anything. If you have reasons to believe X now, and latter those reasons cease to apply, you stop believing. Though it sounds pretty common sense, if applied with enough intensity this principle basically makes the individual unpredictable.
Unpredictability, in light of the law of required variety, means competing with this individual is a red-queen affair. In other words, the problem posed by such a competition is of exponential intensity instead of linear. Which means that, even if it is not dangerous at the moment, it is bound to become deadly on the long term.
Obviously, this is only a problem if there is, really, a contest. Maybe there is none. In fact, there exists a very distinct locus of contention between both camps, but not an actual competition unless concrete, political motives get involved. While relativists have nothing whatsoever against political motives, everyone agrees that the development of thinking tends to be faster and easier far from those motives, because abstraction is penalized by contact with non-negotiable needs. So, for epistemological reasons, it would be better to solve this issue, and forge an alliance, without policy.
Realists need this one policy, though. The reason is that, at their hearts, those camps are not hypotheses, but attitudes. They are not ideas regarding knowledge, they are ways to live life. As a way to live life, Realism does not accept other options.
Notice that, as an idea, as an hypothesis, Realism is extremely accepting: Accept whatever Reality shows you, it says. Acceptance is actually its motto! But as an attitude, Realism is like any other Theism, just instead of «God» they have «Reality».
To be sure, this is a much more sophisticated form of idealism, that of taking a given idea of «reality» as final arbiter of ideas, much better than most forms of dogmatism, but still a dogma. Which means that most of the time you are not subject to someone who can dump laws over your head, but that ultimately in extremis you have to bend to someone else’s opinion.
Like a recently freed slave that does not know what to do with it’s liberty, Realists get confused when served too strong a dose of Relativism. They are used to submitting to authority (though they find a multitude of names to pretend they are actually submitting to something different), so non serviam sounds new and unknown to them. They simply don’t know what to do. That’s why they are so eager to label any sort of Relativism into recognizable groups, like litcrit or post-modernism or whathaveyou.
Not knowing leads to fear, and fear always leads to strong reactions. So realists pretend that litcrit actually wants to steal their authority, or at least disrespect it — pure overreaction.
Relativism never questions the existence of a naive idea of truth. It just looks at the context.
It could be a peaceful relationship, except for the rabid territoriality of Realists.