The principle of the freedom of speech springs from the necessities of the program of self-government. It is not a Law of Nature or of Reason in the abstract. It is a deduction from the basic American agreement that public issues shall be decided by universal suffrage. A. Meiklejohn (source)
Democracy is a power struggle. The participants in this struggle have to be able to express themselves, to present themselves to the electorate, to create a distinct profile for themselves, and to make the electorate familiar with their political program. That’s one reason why democracy needs freedom of expression. The participants in the power struggle also have to be able to organize and associate in a group that is free from government control, because this allows them to gather strength and have a more influential voice. So they need the freedom of association and the separation of state and society. And for the same reasons they have to be able to meet and demonstrate. So they also need the freedom of assembly. If they want to organize, associate and assemble, it’s because they want to convince new people to join them. And they can’t do that without free speech.
Without the guaranteed right of all citizens to meet collectively, to have access to information, to seek to persuade others, as well as to vote, democracy is meaningless. Democratic rights, in other words, are those individual rights which are necessary to secure popular control over the process of collective decision-making on an ongoing basis. David Beetham (source)
The U.S. Supreme Court (SCOTUS) as well has long recognized that the facilitation of self-government is one of the main goals of free speech and the First Amendment. Take, for example, Mills v Alabama:
Whatever differences may exist about interpretations of the First Amendment, there is practically universal agreement that a major purpose of that Amendment was to protect the free discussion of governmental affairs. (source)
Or Brown v Hartlage:
First Amendment [is] the guardian of our democracy. That Amendment embodies our trust in the free exchange of ideas as the means by which the people are to choose between good ideas and bad, and between candidates for political office. (source)
Or Roth v United States:
The protection given speech and press was fashioned to assure unfettered interchange of ideas for the bringing about of political and social changes desired by the people. (source)
There’s also Justice Louis D. Brandeis famous (concurring) opinion in Whitney v California, in which he described the democratic function of freedom of speech. According to Brandeis, every citizen has the right to
endeavor to make his own opinion concerning laws existing or contemplated, prevail. (source)
Brandeis believed, correctly I think, that free speech is necessary for democracy in three ways:
- to inform the people about the workings and policies of the government (a free press being an important part of freedom of speech)
- to inform the government of the the will of the people (an election – or “vote” – being the voice of the people)
- to allow the people to deliberate, to discuss government policy and the merits of representatives.