An interesting thing happened in the '60s, probably introduced by Louis Althusser, and that is the confluence of Nietzschean doubt with Stalinist arguments. These would be unrepentant Stalinist arguments about things. It was a match that was in a sense destined to be. Nietzsche's radical doubt, which doubts reason itself by arguing that all reason is historical and that therefore no one formulation of it can be true, dovetails with the twists and turns in ideology that Stalinist communism developed in the '30s. It should be noted that if folks really accepted the level of irrationality in the universe that Nietzsche suggests exists that we wouldn't be able to get out of bed and start our car because we'd be afraid that it would blow up. Why would we think that? Well, what's to prevent it from blowing up? Your argument that my car won't likely blow up out of the blue depends on logic and reason that's socially constructed and so does not necessarily have any connection to the real, possible, facts. There are knowns, unknowns, and unknown knowns, as Donald Rumsfeld once said; absence of proof isn't proof of absence.
Now, the type of argument used by folks in the various Communist parties about different crimes being committed against people, including the show trials, was that on the one hand the capitalist press was biased and committed to spreading lies about the Soviet Union, which was true to a certain extent, and that when evidence was presented that there was always some logic stretching way of dismissing it based on a sort of radical doubt as to its validity. When people who had been central figures in the Russian Revolution were accused of being English spies the argument was reversed: how do you know that it's not true? Couldn't there be some way that folks like Bukharin could have been in on a conspiracy to undermine the Soviet Union? How are you so sure that the evidence isn't true?
It's disgraceful that this happened, and thankfully only a few smalish groups exist who use these kinds of arguments, but it appears to have prefigured the trend of radical, total, skepticism that came to the foreground with post-structuralism and deconstruction, the sort of thing that Alan Sokal exposed. Calling critical theory people Stalinists is just silly, though, because although lots of people who went on to write and create post-structuralism read Louis Althusser, who was a dedicated (although heterodox) member of the French Communist Party, very few of them shared his political commitments, with Deleuze and Guattari specifically arguing for a more anarchistic radical politics, for example. But I think that's where the trend of trying to completely discredit people based not on any serious evidence but because they come from a particular class, race, gender, national origin, etc...in this world of pseudo-philosophy comes from. There are plenty of reasons to suggest that folks may not understand something because of their race, class, gender, national origin, but most of them involve actual evidence that a person isn't considering an essential fact or facts that they otherwise would be aware of.
In other words, you don't have to resort to a sort of attempt at a Nietzschean impeachment of a person's credibility to argue for radical causes.
*on edit: I realized that I don't make something that's very essential clear here: on the one hand, the only left groups that actually practice this sort of thing are small, marginalized groups that don't really have that much influence, on the other, the academics who practice this and are shrill about it have about zero presence in actual communities. I've yet seen hardcore professors using semi-Stalinist arguments actually doing something in the real world. But, because academics have more influence in the United States than community organizers or people who are active in their communities they get more attention. Also, they don't seem to be having that much of an effect on students. The folks that I know or have known that really go in for the critical theory stuff nine times out of ten spin off into obscure literary fields, where the influence of the teachers is pretty deflated and the 'radicalness' of it all pretty much pro-forma. The other one out of ten are out there but are usually regarded as fucking crazy by other progressives, lefties, radicals, and concerned community members who they come in contact with.So they aren't indoctrinating us all into being Commie Socialists bwa ha ha ha ha ha! In fact, they're shooting themselves in the foot by being so rigid and unconnected to daily life.