If you want an example of how the brutish mentality of the mob is infecting society, look no further than the public shaming of Dermot Mullan, principal of Our Lady and St Patrick's College, Knock. Mr Mullan made a bad mistake. He copied an article from a personal blog, written a couple of years ago by history teacher Tom Rogers, changed a few details, then passed the article off as his own thoughts in a school newsletter.
Understandably, Tom Rogers was not impressed. He highlighted the issue on Twitter, along with the comment: "Hope his students have got the message - plagiarism is A ok!"
Using the Our Lady and St Patrick's Twitter account, Mr Mullan responded with a swift public apology and an acknowledgement of his misdemeanour: "Tom, we have never met in person or spoken and I have done you a wrong. I apologise. I should have attributed your article. I did have the same experience as a student. I would like to apologise in person if I had your contact details."
Mr Rogers, who is also a columnist with the Times Education Supplement, accepted the apology with good grace and said afterwards that as far as he was concerned, the case was closed. "Everyone makes mistakes, he's acknowledged he's made a mistake, let's move on" - that was his final view on the matter.
There has been a great deal of interest in this unfortunate episode, some of it quite legitimate, with on-air discussions on local radio and reports appearing in London newspapers like the Times and Daily Telegraph. Fair enough: exam plagiarism among students is an incredibly serious issue with severe punishments for offenders if caught - and rightly so.
But then the usual toxic froth of speculation, sneering and arbitrary judgment began on social media. An authority figure caught in error - that's rich meat to the attack dogs. Once they scent blood, they don't let go. And that's where it all gets nasty.
Public shaming is an ancient, vicious tactic, a process of mortification intended to humiliate the unlucky recipient. Now, in our hyper-connected society, the brutal instincts of the online hate mob travel at light-speed.
The author Jon Ronson explored this ugly phenomenon in his book, So You've Been Publicly Shamed. He looked at cases like the young science writer whose career combusted because it emerged that he invented a quote, and the PR woman who made an offensive joke about Aids and subsequently lost her job. In each instance, the punishment the person received was excessive and way out of proportion to the mistake they had made. 'Call-out culture' has had a devastating effect on their lives.
Ronson believes that the impulse to shame people who make mistakes is very destructive. In an interview, he said: "I think it's created a conformist, conservative, fearful surveillance society, like the Stasi, and nobody wants to live in a Stasi state, and that's the world we're quite literally living in. I really don't think I'm overreaching when I say that."
Ruthless intolerance for personal errors, even those - like Mr Mullan's - which have been acknowledged and apologised for, is by no means confined to the wild west of the internet.
On the BBC's Talkback programme, I heard a man called Stephen Elliott, who describes himself as chair of the Parental Alliance for Choice in Education, pursue the argument against Dermot Mullan with unattractive zeal.
The wronged party, Tom Rogers, was willing to let it go, but Mr Elliott was not. He insisted that it "can't end with an apology". I don't know who Mr Elliott represents, but I do wonder what his motive is in pressing for further action and redress. Hasn't the headteacher been humiliated enough?
Look, nobody is questioning that Dermot Mullan showed a serious lapse in judgment, in precisely the area where he should be setting a good example for his pupils. Following this incident, it must have been extremely difficult for him to stand up and face the school, both students and staff, knowing that his authority had been damaged. It was mortifying, I imagine.
But Mr Mullan is also a well-respected head teacher with 40 years' experience in the education sector. He leads one of Northern Ireland's top grammar schools.
When he did his ill-considered cut-and-paste job, he wasn't sitting an exam or writing an essay for an academic journal. All these factors outweigh the error he made.
It is wrong to define people by their mistakes. If we do that, then we're all consigned to be failures.