The object of this Essay is to assert one very simple principle, as entitled to govern absolutely the dealings of society with the individual in the way of compulsion and control, whether the means used be physical force in the form of legal penalties, or the moral coercion of public opinion. That principle is, that the sole end for which mankind are warranted, individually or collectively in interfering with the liberty of action of any of their number, is self-protection. That 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.
Note that the harm principle applies to 'compulsion and control' generally; Mill does not restrict it to government action. It would include acts like voluntary public shaming and shunning. In modern Western societies there are currently no major political groups that accept this principle. Conservatives have historically either not accepted it or only accepted it with major qualifications. It is inconsistent with typical Socialist or Green-style progressivist politics. Liberals do not generally seem to accept it. Even Libertarians, who do affirm a harm principle, only do so for government. It is really remarkable, actually, that Mill's harm principle keeps popping up in more abstract discussions of politics and in political philosophy given that everybody these days seems to think it obviously wrong.
I was put in mind of this by this recent xkcd comic:
This is one possible account of the right to free speech (one historically associated with libertarians in particular); it would not be a Millian or classical liberal account. This is somewhat interesting because there's an argument to be made that historically the right to free speech was often understood in broadly Millian terms: the arguments that guided how one understood the right to free speech in the government case were in reality more general principles about freedom of speech that did not exclude 'moral coercion' like bans, and so forth. What's more, it's not difficult to find people still understanding the right to free speech in this way, even if they are not consistent: the political self-expression movement, for instance, tends not to make sharp distinctions between what the government is doing and what society as a whole is doing to interfere with political self-expression, and it's not difficult in the United States to find people who will claim that such coercive measures are contrary at least to the spirit and principle of the First Amendment even if not strictly contrary to the letter of that law. One way one could interpret this is as the fading residue and remnant of the earlier understanding. If this is in fact the case, it would be interesting to look at the history of the collapse of the Millian approach to free speech and what factors were involved.
Of course, as I noted in the previous post, Mill's liberalism was itself an innovation, so perhaps we're really getting the dominance of an idea that was always there, and that it's really more a story of this idea slowly pushing classical liberalism even out of the honorary position of receiving lip service that it had through the influence of Mill. Any number of other things could be going on, too, of course.