So, the original question was "Why is society and culture in the shitter," and my answer was "Kant and his philosophical henchmen." I think the Enlightenment was going in the right direction, but there was a lot of not-so-great stuff there, too. So the Enlightenment is kind of secondary to the point I'm trying to make.

Basically, there were two high points in Western society: ancient Greece, and the Renaissance/Enlightenment* era. Right now, we're not on a high point, and the slope is negative. That's because of the philosophers like Kant that came towards the end of the Renaissance/Enlightenment era.

You are actually focusing on the politics of the Enlightenment, but I'm more concerned with how Kant eventually underminded culture by corrupting things on more fundamental levels. Specifically, the metaphysical level (especially the metaphysics of man) and the epistemological level (especially the functioning of man's mind).

I'm an Objectivist (i.e., I agree with Ayn Rand's philosophy). I know this isn't a popular stance, but extremely few people who criticize it (or even who profess it in the popular media) actually know what it entails, and world-changing ideas are usually universally ridiculed at first, so I hope you'll take me seriously, despite the unpopularity of the ideas I agree with.

So the elevator version is: Ayn Rand is a direct and complete rebuttal to Kant (though not written directly in that manner). You'll have to read her extensively to get the actual rebuttal. As far as supporting the claim that Kant ended the best period in Western history, Rand states this kind of thing, but doesn't try to prove it. Later people (specifically, Leonard Peikoff) have taken up that challenge.

Among other things, Rand holds that man can perceive reality and (ultimately) gain knowledge about it, starting via sense perception. Kant held that sense perception itself acts as a filter that makes true knowledge of reality entirely impossible, basically rendering man's mind impotent.

Rand also has a unique theory of concept-formation, which is critical to establishing a solid epistemology.

Finally, Rand's ethical theory is based on the idea that the is-ought gap can actually be bridged; what is good is what is good for a man. This eventually leads to an actual justification for needing to impose individual rights (in the classic, Founding Fathers sense).

Kant was completely against all the above, and actually made the rise of Nazism, Marxism, postmodernism, and modern egalitarianism possible. In fact, I just though of this, but it's probably right to say that modern "humanistic" political thought is basically a reaction to fascism, but (unfortunately) still within the underlying paradigm Kant made possible.

For example, you need to believe that man has no access to true reality, to believe in dialectical materialism. Same thing to believe in the kind of Nazi racism and nationalism that was rooted in the ideas of the "German subconsciousness".

To elaborate on that: For Kant, the "reality" we experience was created by people's minds. So the German reality (or even the "proletarian" reality) is fundamentally different and incompatible with other "realities," and the only "proof" you need to assert that it is superior is bald assertion that it is so. I do think I'm essentializing a bit here; for example, other people after Kant took his more fundamental ideas to their logical conclusions in ways that may actually contradict other things Kant wrote, and other philosophers helped pave the way for Kant himself.

Anyway, this is just my best (condensed) understanding. I hope to whet your appetite, but don't take me as a representative of other people's ideas.

* And the high point of that era was the founding of the United States, which was the first country to be founded on the idea of the individual as sovereign.