tldr; Public discussions carry too much risk if you discuss anything honestly, you get brigaded or doxed, or things are taken out of context or re-framed by someone based on their own biases of "what you really meant". So people have gone more towards sharing their views or having honest discussions in smaller more trusted groups.
https://danielmiessler.com/blog/the-intellectual-dark-web-is...
tldr; Public discussions carry too much risk if you discuss anything honestly, you get brigaded or doxed, or things are taken out of context or re-framed by someone based on their own biases of "what you really meant". So people have gone more towards sharing their views or having honest discussions in smaller more trusted groups.