Is it John Stuart Mill’s fault that he is overrated? Not necessarily. This great liberal did say, after all, that a once-vibrant system of thought can eventually become a hollowed-out set of prejudices: ‘dead dogma’.

Almost all well-educated people, Mill argued, hold their opinions in ignorance. They have not troubled to think through the arguments for their views; and “they have never thrown themselves into the mental position of those who think differently from them, and considered what such persons may have to say”. Mill thought that in his time this was largely true of Christianity; in our time, it is largely true of liberalism. 

A liberal who did want to investigate the roots of his beliefs might turn to Mill’s hugely influential essay On Liberty, whose 150th anniversary it is this year. The tributes have been generous. Someone claimed in The Guardian that “The principles of On Liberty can bring us together on the basis of our common humanity”. Someone else said in the Independent that “Mill’s words should be our words”.

We should certainly admire Mill, not least for his intellectual courage and the clarity of his writing. But On Liberty itself needs to be challenged. Here is the core of its argument: “The only purpose for which power can be rightfully exercised over any member of a civilised community, against his will, is to prevent harm to others.” You have probably heard that quoted, usually with the implication that it is impossible to dispute.

But it is difficult to say what “harm to others” might be. The porn-user, irritated by his conscience, might well tell himself that what he is doing doesn’t harm anyone else. But as feminists point out, he goes back into his community with a much less healthy attitude to others, especially to women. That is harm, is it not? Drug-taking has similar consequences: there is manifestly a difference between a city where 5% of the population take drugs and one where the figure is 25%.

In fact, everything we do affects our society; and it is hard to use Mill’s principle unless you think – to borrow the words of another overrated individual – that there is no such thing as society. Mill’s Victorian opponents noticed that point; so have some modern left-wingers, such as John Gray, who, despite being the author of Mill on Liberty: A Defence, admitted that On Liberty’s central thesis is ‘a ruinous failure’.

Mill emphasised freedom of choice above all, as a means to human flourishing. But we do not really experience life as a series of choices. We were never given a choice about which society to grow up in, which family to be born into, which political system to be a part of; and we have very little choice about the nature of the institutions (the University of Cambridge, for instance) to which we belong.

Freedom of choice does not amount to much without the inner freedom of being reconciled to these unchosen accidents; and we cannot flourish without drawing on our culture’s vast resources, its customs, institutions and collective knowledge. These are the deepest and hardest questions in politics; anyone who wants to pretend that political aims are easily defined will find in On Liberty a comforting voice.