The three words I would use to describe liberalism are humility, tolerance, and optimism. Humility, because liberals believe that no single person has all of the answers; tolerance, for the same reason; and optimism, because the free flow of ideas will ultimately result in the discovery and common embrace of the truth. As a result, freedom of speech is an essential component of liberal democracy.
Historically, however, the negative impacts of free speech have been mitigated by the presence of gatekeepers and by time; if you wanted to say something false and inflammatory in public, you had to take the time to reflect and compose a letter to the editor of the local newspaper, who would probably refuse to print it. Social media eliminate both of those mitigating factors. Dangerous lies can spread around the world faster than the truth can catch up. What becomes of liberalism then?
Without at least some sort of limited consensus on what is acceptable and unacceptable speech, liberals are struggling mightily to find an answer to that question. For reactionaries and progressives, however, there is no difficulty; if you don’t like a particular kind of speech, you just ban it. The simplicity of that approach gives them an advantage, but it is a danger to our political system.