Stanford encyclopedia of philosophy:

This entry explores the topic of free speech. It starts with a general discussion of freedom in relation to speech and then moves on to examine one of the first and best defenses of free speech, based on the harm principle. This provides a useful starting point for further digressions on the subject. The discussion moves on from the harm principle to assess the argument that speech can be limited because it causes offense rather than direct harm. I then examine arguments that suggest speech can be limited for reasons of democratic equality. I finish with an examination of paternalistic and moralistic reasons against protecting speech, and a reassessment of the harm principle.