There is a limit to the legitimate interference of collective opinion with individual independence; and to find that limit, and maintain it against encroachment, is as indispensable to a good condition of human affairs, as protection against political despotism.
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.
His own good, either physical or moral, is not a sufficient warrant. He cannot rightfully be compelled to do, or forbear, because it will be better for him to do so, because it will make him happier, because, in the opinions of others, to do so would be wise, or even right.
These are good reasons for remonstrating with him, or reasoning with him, or persuading him, or entreating him, but not for compelling him, or visiting him with any evil, in case he do otherwise.
To justify that, the conduct from which it is desired to deter him must be calculated to produce evil to some one else. The only part of the conduct of any one, for which he is amenable to society, is that which concerns others.
In the part which merely concerns himself, his independence is, of right, absolute. Over himself, over his own body and mind, the individual is sovereign.
John Stuart Mill (1806 - 1873)
Mill lays down a simple principle to govern the use of coercion (coercion here covering both legal penalty and pressure of public opinion). We may only coerce others in self-defence - either to defend ourselves, or to defend others from harm.
This rules out paternalistic interventions to save people from themselves, and idealistic interventions to make people behave in some 'better' way.
Politicians take note!