And once Leftist narratives were challenged on those lines, and quickly debunked... in the 1870's... they became mere articles of faith by people who claimed to be intellectuals and faithless.

Along these lines, it is why basically every iteration of Communism/Socialism since 1914 has been increasingly convoluted and insane ways of denying the fact that Marx was wrong and his theories were proven wrong in overwhelming numbers.

Because according to Marx, when World War 1 began breaking out, the workers of the world would recognized their shared solidarity and overthrow their bourgeois and monarchist masters. Instead, they signed up by the millions to go kill each other for king and country, and the only one to fall to Marxist ideals was the ultra-conservative, backward nation of peasants (instead of the industrial titans Marx promised).

And since then, the Socialist who didnt suffer an existential crisis from this have been trying in increasingly more desperate ways to prove they arent wrong, from arguing people's comforts were brainwashing them, to saying they were too stupid to understand and must be lead by the nose by their enlightened betters, to just accepting Nationalism was a fact and how do we work from there.