You make people smarter, and you make the world easier to operate in if you're not smart.
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.
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.