What are some effects of censorship or lack of free speech on a society? This question is based on the book Fahrenheit 451.

I think one effect of censorship on a society is a society that quite possibly winds up being quite ignorant.  Part of free speech, by intention or not, is the attitude that people have a right to know about something.  But if a society were created that never knew about the possibility of being told critical information, then the society would never care to know.  A society that doesn't care to know is a docile society, and it is easy to rule over.  It's easy to rule over, because the society always assumes that whatever information is coming from the powers that be is good and correct information.  Any other contrasting information has been censored, so there is never any reason to question the info being given.  That's what happened in Fahrenheit 451.  Without the books and the ideas that they contained, the society quickly became ignorant of other lines of thought.  Once that happened, the entire society became like Montag's wife.