famous for his work "On Liberty",
any form of power that can legitimately be exerted upon an individual is solely for the purpose of protecting the rights of liberty of others ("The only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others."),
also known as the harm principle,
it should be noted that Mill explicitly states that the harm principle does not apply to harming oneself either morally or physically "[state intervention for] His own good, either physical or moral, is not a sufficient warrant."
only individuals can determine from themselves what makes them happy,
freedom of speech is the path to truth,
fullest liberty of expression is required to push the boundaries of logical argumentation rather than the limits of social embarrassment,
truth evolves with time,
free discussion should prevent "deep slumber of a decided opinion" (interesting reference to echo-chambers in an early stage definition),
neither economic, moral implications nor the speaker's own well-being should justify suppression of speech,
the only instance in which free speech can be suppressed is only in case there is a clear and direct threat (harm principle)