Freedom of speech has always been the right of every citizens, everyone is allowed to express their opinion and thought towards something but now things have changed, we can't speech freely fear of the government, or what if someone is hearing.
In most countries a lot of people get killed just because of their speech against the government, against the society.
So in this case people are force to control their speech most especially the civil servants, government workers cause if they speak bad against the government they'll be sack from their job, so in my opinion the government are responsible when it comes to limitation of speech, cause when everyone keeps fearing the government then they're the issue.
Though I do not completely share the same position as you, I can agree with you say the government or the established powers are those who are mainly responsible for the lack of free speech and responsibly for the punishments against those who want to speak freely about topics which are very sensitive to those same established powers.
One only needs to take a look at countries like Saudi Arabia or even Venezuela.
One could easily end up in prison for either saying something against the Sharia law or against the corrupt politicians from any Republic in decadence.
When those in positions of power start to censor one's speech it may be just the beginning of an escalation towards a more authoritarian way of living.