Censorship: Has there ever been a case in history where restricting what adults can say or read has lead to a positive outcome or can be viewed as a positive?

The answer depends a lot on one's definition of "positive". Humans are the only known animals that "build" on knowledge over multiple generations. If you think in terms of decision trees, full freedom of speech/choice lets humans explore the full width of any decision tree. In the long term that is almost always positive. However, exploring all nodes width-wise, including ones that may be viewed by a large majority as unnecessary/pernicious may exhaust the limited "thought" resources of a community or society and may prevent exploring those paths considered as necessary/beneficial in sufficient depth. So sometimes, limiting the node search may bring benefits in the short term. Stepping out of theory, look at the expansion of Islam in its initial years. It was achieved by a ruthless suppression of all competing ideologies in Arabia. The subsequent religious/social stability, led to formation of a formidable military machine as well as significant advancement of Arabic scientific thought and culture. Was that something that is truly "positive"? Were there valuable philosophies or cultures that were forever lost in that process? It is a matter of perspective   EDIT: I got a little bit confused by the Anonymous comment below which seemed to indicate that I viewed the nature and methods of Islamic expansion as positive. I am in no way condoning those.   The point I was trying to make is that humans are naturally curious and innovative, and build knowledge over successive generations. So when you restrict what adults can say or read, as mentioned in the question, it does not stop all human progress. All it does is focus or limit any progress to the narrow confines of what is acceptable/allowed. In case of religion, instead of a truly open philosophical search, it assumes the established religious/philosophical framework as a given, and limits philosophical discussion to (say) how should verse X on page Y of book Z be interpreted in a certain situation, which may or may not be a "positive" based on your perspective.   Maybe a more apt example is a totalitarian regime like North Korea. By severely limiting freedom of thought and expression, they have achieved an entire society that is unquestioningly dedicated to the North Korean cause and one that focusses all its energy to the preservation of the North Korean state. From a free world perspective - it is a "negative". From the perspective of the Kims and their established power structure, it is a "positive", and exactly what they intended to achieve in the first place.