They are unified only by a single opposite, which is itself a straw man - his past monolithic authority as us against them and us should win. With nothing imagined as a consequence of "winning" but survival for one and disappearence for the other. Measured by that straw man - itself a piece of 19th century pseudoscience - anything that allows the survival of multiple types appears as one thing.
And all the distinctions between versions of it thus disappear. This amounts to posing an exclusive disjunction between totalitarianism and relativism - when the evidence of the entire past, down to quite recent times, refutes the idea that the two exhaust the possibilities. It predicts that as you scan history you will either find one monolithic block, or will find full blown relativism. And this isn't remotely true, as mere historical fact.
Tolerance is not relativism. Relativism denies the existence of one truth. Tolerance does not. Relativism denies that anyone's notions of right and wrong could actually be mistaken. Tolerance does not. The hidden minor premise of this totalitarian-relativist dicotomy is that the truth would deserve to be made mandatory if it existed and were accessible, while error would deserve to be exterminated. The thesis of tolerance, to the contrary, is that error is not crime, and that truth can only be the subject of an invitation, not of a command.
Tolerance expects many views to exist indefinitely. There is nothing annihilationist about it. From the standpoint of the real principle of tolerance, the relativists aren't remotely tolerant enough. They only tolerate where they cannot show error. Tolerance is tolerance of error, real full blown known-to-a-certainty error, or it doesn't deserve the name. On the side of the tolerated, it is not an imperfection in ruling truth claims that it all hangs on. No, tolerance is a right to be wrong.
In the sense of mistaken, incorrect, or uninformed. In lesser matters, also in the moral sense, as weak, timid, or flawed. Beyond error there is a different category entirely, the category of crime. And error is not crime. Crime is also possibly from a position of correctness or truth. The two concepts are in fact at right angles to one another. One concerns the justice of our behavior toward our fellows. The other concerns not justice, but the adequacy of our mental representations and systems of symbols to the rest of the world, to the real relations they point toward.
Why are they so frequently confused? Because historically, certain sects at definite times and places attempted to criminalize what they regarded as errors of doctrine. They imputed all mistakes to willful error.
There is a marvelous passage in a medieval Islamic book that brings this out. Averroes objects to holding philosophic writers responsible for their mistakes about recondite matters of metaphysics (by banning their books or worse), pleading that giving one's assent to an indication within the soul is involuntary. This is as close as Islamic thought came to the later principle of tolerance. Then in less than two pages he turns clean around and declares that error by anyone except a learned philosopher while dealing with the most difficult subjects, is "sheer sin".
That is on the subject of theoretical error. Moral error is in a way more serious. It is moral judgment that gives the relativist types the willies. When Bush calls evil men and regimes evil as a matter of course, they freak. They don't understand chastising something to improve it - despite Brin's claim that relativist pluralism is open to that, the reality is you can't chastise anything without a definite standard for it to fail to live up to. Only moralists can chastise things. Pluralists just slink away and start a new fashion. Which might make a few more flowers bloom but does nothing to improve the older ones that aren't blooming.
To improve something, you have to be moralist enough to condemn its present state. But you also have to be attached enough to that thing that you consider it worthy of the trouble. The relativists of Brin's variety, or the young woman in my anecdote, aren't moralist enough to condemn the present state of Islamic political culture. The state department cynics who think tyranny is the natural government of Muslims aren't attached enough to any of it to think it worth any effort. A Bernard Lewis, on the other hand, sees the contrast between a once flourishing civilization and the present moral squalor, and chastises. He has an attachment not to their present state, but to what he thinks it could be.
Which is where all real moral reform must come from. But does our own culture teach this, successfully? It does not. It teaches it more successfully in practical life than in philosophy, but it falls short in both places. Academic types are short changed on the former and get triple doses of the latter.
The relativist left has been on a mission for several decades now, to rid us all of the scourge of power by first taking away our power of conviction. Emphatically it does not work. But the attempt leaves behind a peculiar trail of moral cripples, and a peculiar sort of moralized divide within the society that has attempted it.
Half of our people that by training and temper should be pillars of moral purpose, are at best useless and frequently worse than useless. Every instinct that young woman had was just. All her personal conduct was spotless, generous, even chivalrous. And it was all ashes, because of this prior error. The heart was sound, the head was broken, and the result was a maimed thing where there should have been a wonderful thing.
Notice that this is the opposite of the diagnosis others often have of us, or of much of the modern left, or of intellectuals in particular. Too sophisticated and not moral enough, middle America imagines. In one sense of "sophist-icated", a fair enough charge. But in many cases, not half sophisticated enough, intellectually.
Now notice, here too the principle of tolerance applies. These people are in error, but many of them aren't at all criminal. It would be ruin to follow their cracked heads, to be sure. But we must tolerate their error while trying to correct it. That means chastise them and call them to something better, but with an underlying attachment to them as fellow citizens and as people. Of exactly the same sort Lewis shows toward the Muslim world.
Conversion of the adversary is the missing term in Brin, above (and with it, human unity). At bottom, it is not a competition or a fight. At bottom, we are allies, in a war with our own limitations, both moral and intellectual. The "we" in that statement does not stop at the water's edge.
It is a pleasure to be able to talk about these things...