from John Stewart Mill, On Liberty, l867

"If all mankind minus one, were of one opinion and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person, than he, if he had the power, would be justified in silencing mankind."

Here are several general points that he makes in the body of his essay.

I.                    If an opinion is silenced a truth might be silenced.

II.                 Even an erroneous opinion may hold some particle of truth or may be helpful in ascertaining the truth.

III.       Unless an opinion held is challenged or contested it becomes little more than a prejudice held. 

IV.       Without challenge opinions (especially those commonly and reflexively assumed to be true) can become lifeless and flaccid.
 

V.         Ideas most likely to be suppressed are those most likely to contain a grain of truth that should be heard.
 

VI.         Repression of the timid harms society (making belief depend on strength rather than truth).

And here are a few quotes from the essay for thought and debate..

"All silencing of discussion is an assumption of infallibility." (By those calling for the silence.)

"Strange it is that men should admit the validity of the arguments for free discussion,

but object to their being pushed to an extreme, not seeing that unless the reasons are

good for an extreme case, they are not good for any case."

"He who knows only his own side of the case knows little of that."

"Protection . . . against the tyranny of the magistrate is not enough; there needs protection against the tyranny of the prevailing opinion . . . and against the tendency of society to impose, by any other means than civil penalties, its own ideas and practices as rules of conduct on those who dissent from them."

"If the teachers of mankind are to be cognizant of all that they ought to know,

everything must be free to be written and published without restraint."

There are at least two caveats that should be noted.  Mill had no intention to make this statement applicable to those who were not mature in their faculties. He also did not think that the barbarians who lived in backward societies should be given the same kind of liberties as the more enlightened and civilized British.