There is a biological, survival-motivated reason behind the fact that we are verbal, social herd animals.
Thought, speech, dialogue and the market are learning mechanisms to weed out dangerous ideas. The prefrontal cortex was born out of the motor cortex, and is where rationality lives.
This applies to political structures, economies, social justice movements, parent-child relationships, friendships, marriages, inventions, business strategy, religion, law, and philosophy.
Without free speech, there is no clear thinking.
Listen to three minute explanation here: