I struggle to get this. "Dumb" people feel threatened when others can freely express themselves?
Lets imagine a workplace with two teams with two not very intelligent leaders, and two intelligent up and comer. One team leader goes "I'm open for suggestion, talk to other teams, talk to my boss" and he's replaced in a year. The other boss goes "We need to enforce a hierarchy, only juniors speak to seniors, only seniors speak to me, only I speak to other teams" he might have that job for YEARS as the other managers go "wow that guy suddenly started delivering results and I thought he was dumb, I guess I was wrong".
If you imagine both team leaders are smart, than the smart team leader who allowed open communication will probably outperform the one who didn't since they're not threatened by the junior regardless.
If you're not very smart, coming up with ways to make people less free to speak can show wisdom.
Quite a lot of the laws around restriction of speech are specifically designed to stop smart people from exploiting less smart people. Smart people have to be censored or they will hurt less smart people.
The idea that someone has their “own truth” separate from the rest of the universe is one of the most absurd ideas in pop culture, imho. That a large portion of the population considers their perception universal reality makes it difficult to progress culturally.
Determining and disseminating truth is not straight forward but abdicating to relativism feels like devolving to the Middle Ages.
As you say, determining and disseminating truth is not straight forward and I think you really have to read between the lines when you hear people say things like "Hear her truth" is that these are often people who allege certain classes of people have long had their actual testimony ignored by society because of who they are. Also most of the time people say this, they're saying this regarding fundamentally uncertain situations where uninvolved parties can never be 100% sure of the truth. So there is a political/practical/contextual aspect to these epistemological statements.
You make people smarter, and you make the world easier to operate in if you're not smart.