My impression was more "All models are wrong, therefore all models are valid". Some models are less wrong!
It seems to me that the postmodernism movement correctly called attention to social models being somewhat arbitrary and power-based but then (motivated by ideological agendas?) ran with the ball to say this means all cultures are equally worthy (where worthy means "should be promoted").
To use an exaggerated example, I cannot accept that eg an oppressive ultrareligious culture that practices infanticide, genital mutilation and wife beating is equally as worthy as eg a peace-and-love hippie commune. A philosophy devoid of value judgements is just nihilism wearing different pants.
I hope you realize the irony of complaining about the notion that viewpoints are equally worthy when you base your complaint in... your own viewpoint about what postmodernism means to you.
But no, I think you'll find practitioners of postmodernism are perfectly capable of making value judgments. They just make using different frameworks and different criteria than the the people who came before them.
> My impression was more "All models are wrong, therefore all models are valid".
That's a misrepresentation. It's actually fairly interesting where that misrepresentation originated from (hint: it was propaganda from totalitarian movements).
It's a reaction to modernist assumption that "absolute truth" is possible for any question, and in particular, how often that truth _just happened_ to be personal taste of some dude (brutalism (I personally like brutalism) and modernist architecture in general are probably the most obvious examples).
For sure, there have been explorations into pretty much every field, with varying success. In science, though, that relativity is more oriented towards establishing what theories get investigated, than the actual result (for example, how many investigations of liberalism in political science completely ignored the racial aspect of it, and its rather dismal history in that respect, or various - thankfully largely defunct by now - excustions into phrenology, eugenics, and similar woo).
So, modernism isn't "all models are valid." It's "you can't just declare that your model is the bestest because you like it/it's 'simple'/it's 'elegant'/it happens to declare Helvetica to be the objectively best font."
It seems to me that the postmodernism movement correctly called attention to social models being somewhat arbitrary and power-based but then (motivated by ideological agendas?) ran with the ball to say this means all cultures are equally worthy (where worthy means "should be promoted").
To use an exaggerated example, I cannot accept that eg an oppressive ultrareligious culture that practices infanticide, genital mutilation and wife beating is equally as worthy as eg a peace-and-love hippie commune. A philosophy devoid of value judgements is just nihilism wearing different pants.