Imagine the conversation that must have been going on in the household of the Nobel Prize-winning scientist Sir Tim Hunt and his wife, the immunologist Professor Mary Collins, in the past 24 hours.

There's been a suggestion that, after the scandal that erupted over his unwise comments about the emotional hazards of mixed-sex labs, and his subsequent resignation, University College London might consider taking him back.

The real scandal, of course, is that he was asked to resign in the first place. He should be reinstated forthwith, and with a fanfare of apology for the ignominy he has had to endure, and the devastation to his distinguished career. And all for what? A few thoughtless words about the fact that men and women have a tendency to fall for each other when they work together, and that women sometimes blub when criticised? Clearly, this has been his experience, and he will not be alone. Nor, having done both things in my time, can I see what is so terrible about what he said. Patronising - yes. Belittling? That too. But spoken at a dinner party, or over a drink in a bar, Sir Tim's remarks would have barely registered, let alone seriously offended anyone who heard the mild, old-fashioned manner in which they were uttered. With men of his ilk, the best response is to patronise back, responding not with a howitzer, but a lemony smile. Those lab scientists who responded by tweeting images of themselves looking "distractingly sexy" in full-body protective clothing had the right idea, laughing at themselves as well as Sir Tim.

Indeed, compared with what one hears almost every day on the bus or in the street his chauvinism is almost gentlemanly, the outlook of a boffin who has been in an ivory tower for most of his life, more concerned about the contents of a test-tube than of the latest report into on-going gender inequality. The woman who tweeted his words from the conference in South Korea cannot have anticipated the furore that followed, but she was obviously hoping for a response. Unlike his off the cuff joke, this was not an innocent or unthinking act. Anyone who ever speaks in public other than from an autocue will have shuddered to see the result. Today, the slightest slip of the tongue, off-colour remark or un-PC utterance can cause a firestorm. Think of Benedict Cummerbatch, roasted like a chestnut for using the word 'coloured' when protesting about the lack of good roles for black actors. It'll be a long time before others speak out on the same subject.

Thanks to the bullying potential of twitter, where zealots can whip up a like-minded crowd in minutes, being offended has almost become a new sport. Despite the fact that we are better educated than ever before, our skins seem to have grown thinner, our mob instincts stronger. It's a toxic combination. Pity the poor soul who becomes the latest witch in this very modern form of persecution. Victims may not be burned at the stake, but they are emotionally flayed.

One of the most shocking aspects of this unedifying episode is that it is the work of a highly respected university, a place that, rather than respond with hysteria to tweets in a teacup, ought to have shown itself a model of lofty principle. Higher education is about learning to think for yourself, not follow the herd. If a place that ought to be a bastion of liberal philosophy, one of whose main tenets is freedom of speech, can be so easily swayed by public opinion, then we have reason to be alarmed.

The growing climate of censoriousness is particularly distasteful given that freedom of expression is already under attack. Witness the outcry after the Charlie Hebdo killings, when heads of state and other figureheads endorsed the unassailable right for those of us in the democratic world to say what we think. Whatever the subject matter. Even if it gives offence. The alternative - a spiral that starts with self-censorship, descends into state control, and ends with persecution and execution - is unthinkable. Yet as Sir Tim's peccadillo suggests, the Thought Police, those guardians of ultra-political correctness, are on the watch wherever we go. The message is frighteningly clear: we are no longer really free to say what we think, prejudiced or crass or unintentional though it might be.

The bad old days of flogging, hanging and deportation might feel unimaginably far-off, but with the rise of "group think", aided by social media and its protective cloak of anonymity, we are witnessing a trend that could become almost as punitive. Tolerance is and must remain the very keystone of civilisation, extended to everyone, including the politically incorrect. Obviously I'm sorry if that fact bothers anyone. But not very.