Under nearly every theory of free speech, the right to free speech is at its core the right to communicate to persuade and to inform people through the content of ones message. The right must also generally include in considerable measure the right to offend people through that content, since much speech that persuades some people also offends others.
Persuading and informing people may certainly cause harm; the listeners might be persuaded to do harmful things. But the premise of modern First Amendment law is that the government generally may not (with a few narrow exceptions) punish speech because of a fear, even a justified fear, that people will make the wrong decisions based on that speech: [T]he people in our democracy are entrusted with the responsibility for judging and evaluating the relative merits of conflicting arguments....
f there be any danger that the people cannot evaluate the information and arguments advanced by [speakers], it is a danger contemplated by the Framers of the First Amendment. Thus, punishing speech because its content persuades, informs, or offends especially conflicts with the free speech guarantee, more so than punishing speech for reasons unrelated to its potential persuasive, informative, or offensive effect.
The Volokh Conspiracy - Content-Based Speech Restrictions vs. Content-Neutral Speech Restrictions:
