Rooting through the recent archives at Jim Kalb's Turnabout, I came across this:
Scientific knowledge is knowledge of mechanism that enables prediction and control. If you treat that kind of knowledge as adequate to all reality, which scientism has to do to be workable, then human agency disappears.
Human agency is nonetheless with us. We know ourselves as agents, we recognize others as such (if we are not psychopaths), and intelligent activities like science seem to require it.
The solution people adopt is to accept human agency as a reality but a very strange sort of reality about which nothing can be said. To say something about it would be to assert knowledge regarding it and therefore to attempt to subject it to a regime of mechanism, prediction, and control. That’s why it’s horribly wrong (in the current view) to classify people or to attribute significant qualities to them. Any attempt to do so is an attempt to enslave them.
Instead, each of us becomes equally an unknowable being transcending all reality about whom nothing can be said and whose will has a validity to which no limits can be assigned. But then science stops being the supreme standard. PC becomes the supreme standard. Each of us becomes a god, absolute and unknowable. If that conflicts with science, so much the worse for science, and that is where we are today.
The moral: science is a wonderful thing, but it’s a specialized part of more general human practices of knowledge, and when it tries to be the whole you get big problems.
When you subscribe to any kind of metaphysical system based on error (i.e., the self-refutingly unscientific belief that science is the only way to know things), that's what you get: "big problems."
A system of thought can run aground in two respects. First, it can be simply self-contradicting, which is to say that it can't possibly true because it refutes itself. Scientism, I've argued before, is one example of this, but so too is what I've previously identified as deontological libertarianism -- in a nutshell, the belief that consent is morally prior to all other arrangements (whether or not you consent to the binding character of your consent). I'm sure you can think of other systems of thought that truck-bomb themselves right out of the gate (e.g., "all truths are relative"). If you can gather up all the loose ends, you might be able to tie them together into a single act of circular reasoning ("the right to property derives from the fact of self-ownership; the fact of self-ownership is legitimated by the right to own things"), but that doesn't resolve the problem of internal consistency.
The other respect is that it can contradict intuitively-apprehended first principles. As I wrote yesterday morning on Catholic Complementarian (which I recently discovered and now enjoy immensely) with respect to liberal hysteria over pedophilia:
. . . liberalism is at best highly inconsistent re: its attitude toward sex and more often than not treats it like it does everything else, within a paradigm of materialist reductionism: it’s “just sex.” Innately meaningless, valueless, a totally physical recreation with at best conventional (and thus arbitrary) significance attached to it. Yes, sex is regarded as an expression of the self, but so is everything: piercings, tattoos, desecrating the Eucharist, etc. And it regards it as no more innately valuable or meaningful than any of those things.
So to answer your last question, “Why the liberal hysteria over pedophilia?” you have to bear this in mind… that if sex is meaningless, than sexual crimes must also be meaningless. In other words, reflexive hysteria and the Voegelinian prohibition of questioning is their way of confronting the fact that a world filled with pedophiles is exactly what a world run consistently on their principles would look like.
(It's a credit, actually, to the basic decency of people that modernity has taken so long to get to where it is. The shucking of long-held moral convictions, even in the face of inability to articulate rational defenses of them, is difficult. One has to convince oneself. It's a testimony to what Christians have been saying all along -- that man has an intuitive and innate yearning for the good -- that modernity can only function because it's riven with unprincipled exceptions from its own logical conclusions. Yeah, the modern objection to pedophilia is basically irrational within the framework of its own principles; yeah, they can't explain why instinctive revulsion is OK with respect to pedophilia but not OK with respect to homosexuality [bearing in mind that "because they can't consent!" hasn't ever stopped us from making them eat vegetables, brush their teeth, or do their homework, or that people don't respond with horror to violations of legal technicalities]. But moderns are basically decent enough [for now] that they don't let their irrational dogma get in the way of the intuitive apprehension that buggering children is wrong, and not just because they're technically, legally incapable of consenting until they reach an arbitrarily-designated age.)
So unsound systems of thought produce big problems. But the system of thought characteristic of modernity -- basically ontological reductionism, the war against the order of being -- is a big thing, and it relates to the world in big ways. Its fingers extend not merely through the way we think about being but also the way we think about man, the universe, society, knowledge, and ethics. So the problems it produces aren't just big problems -- they're BIG big problems. As Kalb relates in his talk "PC: The Cultural Antichrist":
. . . political correctness is an odd tendency. It's a bit uncanny. It doesn't fit in with how we normally think about things. That's why we don't know what to make of it. People try to laugh it off, but it doesn't laugh off.
It seems too stupid to be real but it trumps everything all the same. If a thieving employee shoots and murders his co-workers the big question is whether any of them were racists. When an affirmative action army officer does the same, because he wants to do jihad, what top brass worry about is whether it will make diversity look bad.
Something that trumps normal considerations so completely must have transcendent importance. It's clear that PC relates to something big.
(Here he's referring, respectively, to the atrocious headlining of a news story relating to a black employee's murder of eight white coworkers in a shooting spree, and Army Chief of Staff General George Casey's cautioning that the murderous rampage of an affirmative action hire at Fort Hood, Texas, shouldn't lead the Army to deprioritize ethnic diversity).
Ordinarily, egregious errors are self-correcting, if nothing else because their proponents follow them through quickly to obscene and heinous conclusions. What, then, has kept the modern train of errors running? Personal dishonesty and intentionally affected ignorance internally, intentional suppression (libeling, intimidation, and murder) of people who presume to point out the errors as errors externally. I think this latter point has historically been more important in fueling the compounding errors of modernity, precisely because it fuels the former; the ends seem to justify the means beforehand, but absolutely have to once the fires have started and the graveyards begin to fill.