The passage can be broken down as follows: Premise: Democracy requires no restriction on citizens' ability to share their ideas freely, without fear of reprisal. Subsidiary Conclusion/Premise: Therefore, the right to have private and unmonitored conversations is essential to democracy. (Overall) Conclusion: For a government to monitor Internet conversations would thus setback democracy.
You are correct in identifying "therefore" as an indicator of a conclusion. However, "thus" is also a conclusion indicator.
Here, the second sentence is a conclusion that is supported by the first sentence. However, this second sentence in turn supports a larger conclusion- the last sentence. We call something that is both a conclusion and a premise that supports a larger conclusion a "subsidiary conclusion." That is what the second sentence is.
Does that make sense? Please let us know if you have any additional questions!