George Orwell, 1984
If one grants primacy over their own mental faculties - believing that anybody else's word has more relevance than their very interpretation of the world - then that other group now has the power to make one believe, and ultimately do, anything. At scale, that is a recipe for horrible things.
A society with a freedom of thought will never have a utopia because we just can't stop finding falsehoods appealing. But you will also never have a dystopia because society will always trend towards the truth as the past of least resistance, even if the road there might be quite bumpy. But in the grand scheme of things this is the state mankind has been in that sent us from being glorified apes to to being glorified apes with vast cities, neat toys, and being on the verge of setting out in exploration and settlement of the stars.
"Intellectuals [are] virtually the most vulnerable of all to modern propaganda, for three reasons:
1) they absorb the largest amount of secondhand, unverifiable information;
2) they feel a compelling need to have an opinion on every important question of our time, and thus easily succumb to opinions offered to them by propaganda on all such indigestible pieces of information;
3) they consider themselves capable of 'judging for themselves'.
They literally need propaganda."
Konrad Kellen in the introduction of Propaganda: The Formation of Men's Attitudes by Jacques Ellul