What role should social pressure play in the policing of free speech? Two things I've seen recently pose this question.

One is the racist harassment of Rufaro Chisango at Nottingham Trent University. I like to think that in better places and times those racist twats would have been swiftly suppressed by violent force by fellow students. Ms Chisango would, I suspect, gain much more confidence from knowing that her friends and neighbours have her back than she'd get from having to appeal to slow, impersonal and often incompetent university authorities or the police.

The other is the conviction of Mark Meechan for what seems to have been a bad joke. I agree with Adam Wagner that this is a bad idea. Criminalizing "gross offence" means giving too much power to the police to suppress unpopular ideas or ill-judged language. A more appropriate response would be to either ignore it and condemn such people to obscurity, or to just tell them they are wrong.

Such social pressure has worked well in the case of David Irving. He should be legally free to deny the holocaust, but the rest of us are entitled - and correct - to treat his as a pariah.

I'm even relaxed about most cases of no-platforming. Nobody has a right to speak at (say) a students union, any more than I have a right to a column in the Telegraph. A right to speak does not give the rest of us an obligation to host you.

Nor does that right entail freedom from the consequences of exercising it. You have a right to speak, and the rest of us have a right to tell you forcefully that you're talking shit or to ignore you.

In fact, if the marketplace of ideas is to work, bad ideas must be weeded out. This is done by vigorously opposing them.

All this leads me to think that we should police speech not with the law but with the force of others' opinion - either shunning them or opposing them depending on context.

Except, except, except. Here are four counter-arguments:

- Some privately-provided platforms are so widespread and important that withdrawing them is, as Robert Sharp says, a form of "privatized censorship." He's talking of Facebook's banning of Britain First. They deserve no sympathy, but there's a slippery slope here: if Facebook can ban them, it can - as Robert says - also censor others.

- Private sanctions against speech we don't like can be excessively harsh. For example, I wouldn't want firms to be able to sack employees just because they have opinions their employers don't like.

- There's a point, perhaps not easily defined, at which vigorous and widespread opposition becomes bullying: was Mary Beard bullied after her (I think) ill-judged tweet about "'civilized' values"? I'm not sure. But women are especially vulnerable to an ugly mob rule.

- John Stuart Mill had a point in warning us of the tyranny of the majority. This he wrote, is

more formidable than many kinds of political oppression, since, though not usually upheld by such extreme penalties, it leaves fewer means of escape, penetrating much more deeply into the details of life, and enslaving the soul itself. Protection, therefore, against the tyranny of the magistrate is not enough; there needs protection also against the tyranny of the prevailing opinion and feeling; against the tendency of society to impose, by other means than civil penalties, its own ideas and practices as rules of conduct on those who dissent from them; to fetter the development, and, if possible, prevent the formation, of any individuality not in harmony with its ways, and compel all characters to fashion themselves upon the model of its own. 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.

Like other tyrannies; the mere fear of this power can be repressive. I fear it has led to a diminution of worthwhile opinions such as Oakeshottian conservatism or free market egalitarianism.

My point here is that we face a genuine dilemma. On the one hand, there's much to be said for using social rather than legal sanctions against speech we don't like. But on the other, those sanctions can be as excessive and misapplied as legal ones.

Dilemmas such as these are, I think, under-debated. Everybody is so keen to press their own point of view that we tend to miss a big issue - of how best to create a genuine healthy public discourse in which all voices are heard whilst at the same time ensuring that the marketplace for ideas selects against bad ideas.