I see the post modern situation as depressing because a general theory of progress (e.g. Marxism) or even justice in the abstract (e.g. Rawls or Christianity) doesn't seem possible.
There is a "post human" philosophical movement, interested in things like Schwarzenegger's character from The Terminator, but I think the philosopher and I shared an additional meaning equivalent to "extinction".
I would point to Reason magazine as an example of people using the word "Reason" to create a frame in which people who believe that people have the right to form unions or that the state should regulate pollution or provision health insurance or public schools.
If you withdraw to pure mathematics you'll find Godel, Tarski, Turing proved that there is no salvation in logic.
The collapse of master narratives leave us scrambling for meaning, finding some, but with the feeling the apocalypse happened some time ago (1945?) and we are now living in some movie like Mad Max.
If there is moral rot in postmodern philosophy it is the moral rot of the age which is documented here:
https://en.wikipedia.org/wiki/The_Culture_of_Narcissism
(big in Japan because Japanese people think it describes the Tokugawa culture)
https://www.amazon.com/Cultural-Contradictions-Capitalism-20...
Academically, Marx was ahead of his time even if his prophecy that capitalism would be smashed by "the tendency for the rate of profit to decline" and the labor theory of value turned out to be bunk. He was popular in the 20th centuries and even David Bell chair of the social sciences department of Harvard and as ardent a supporter of the status quo as there ever was claimed to be Marxist. [3]
[1] https://en.wikipedia.org/wiki/Konstantin_Tsiolkovsky [2] https://en.wikipedia.org/wiki/Russian_Futurism [3] https://www.amazon.com/Cultural-Contradictions-Capitalism-20...