There's the moral self-loathing (veering towards self-flagellation) of the 'social justice' class, the academic anti-truth of the relativists and the post-modernists, the equally poisonous know-nothingism of parts of the right.
Western civilization still lives in the long shadow cast by Europe tearing itself apart not just once, but twice in the span of a generation.
So how about some simple, unambiguous fact that should submit to easy verification?
As of late last year, about 42% of Republicans polled disagreed with the assertion that Obama was born in the US, while only 27% of Republicans agreed [1]. Plus the fact that our current sitting president was instrumental in formulating and then popularizing this lie.
I submit this to you as a good example of 'know-nothingism' -- if there's some piece of information that challenges your world view, then you will do your damned best to know nothing about it.
[1] https://www.nbcnews.com/politics/2016-election/poll-persiste...
"Know-nothingism" derives from the Know Nothing party of the late 19th century that was known for its anti-immigration views. The Know Nothings originally held secret meetings and would tell people "I know nothing" when asked about it. So it was not originally a derisive term.
Then starting in the 20th century, nativist political sentiments (and this includes the "America First" mentality espoused by our current president) was called "know-nothingism" by liberal commentators.
So now it has morphed into a term of derision, however it still maintains its attachment to nativism, although anti-intellectualism is obviously a big part of the stereotype.
This is all to say that yes, know-nothingism is sort of a shorthand for Trumpism as far as I can see it, so it's kind of a truism to say that know-nothingism is prevalent on the right. As far as whether it's poisonous, or equally as poisonous as the cultural relativism of the left, I will demur.
Edit: runon and typo
I wonder if this played some role in Kaczynski's strange tragedy. As the article describes, he seemed to have adopted parts of each approach -the moral nihilism and dualism of the sciences, coupled with the anti-technology and anti-empiricism of the humanities. Almost as if he absorbed only those things each camp said to damage the other as true. Of course he ultimately did end up murdering scientists and engineers, so it's clear which side his sympathies fell toward in the end.