"Politically correct mobs are a form of this - they are ugly and indiscriminate, but effective at shaping culture by stigmatizing ideas that have been used to justify harm".
How do you define "harm"? It seems that the modern edition of "progress" is trying to eliminate psychological harm by controlling people's speech. Is psychological harm really something worth trying to eliminate in our society?
I'd argue no. Our society thrives on free speech and truth, and attempting to silence people for the sake of keeping the feelings of others intact is not a trade off that's worth making. A book I read that was very informative on the topic was "The Coddling of the American Mind" by Jonathan Haidt - I'd highly recommend looking into it.