Ambushed on live television with a list of alleged paedophiles in the Conservative Party that was culled from the internet, the Prime Minister cautioned against a "witch-hunt". It was a sadly apposite warning. Britain has, in recent days, flirted alarmingly with the failure to distinguish between accusation and guilt that is one of the nastier hallmarks of mob rule.
There are two issues here. One is the increasingly hysterical preoccupation with paedophilia, particularly the notion of large-scale networks of high-profile public figures abusing children and pulling strings to keep their activities secret. There is no question that recent revelations about the 40-year abusive career of Jimmy Savile are both shocking in themselves and a damning indictment of institutions in which so much went either unseen or unchallenged. But even if signs of trouble must be taken more seriously after Savile's fall from grace, the innocent must remain innocent until proven otherwise.
Similarly, claims that the perpetrators of systematic sexual abuse at a North Wales care home included influential people not tracked down by the subsequent public inquiry cannot be trivialised. The involvement of well-known politicians cannot simply be assumed, however, nor guesses at their identities wantonly exposed.
It is here that the other issue raised by the recent rash of exposures and half-exposures comes in; the question is when – or, indeed, if – the vast swell of gossip, innuendo and outright defamation on the internet should make the leap into the mainstream media.
In handing the Prime Minister a list compiled "in about three minutes" online, Phillip Schofield misjudged the distinction between accusations that require an answer and those that are for the birds. But he is not alone. Just one day later, a newspaper story claimed that internet rumours linking a former adviser to the Thatcher government to the North Wales abuse scandal was a case of mistaken identity – naming the victim, Lord McAlpine, in the process.
There is one halfway plausible explanation. If the assumption is that everyone is now online, and that the roar of chatter on the internet is unavoidable, perhaps the new role of the mainstream media is to act as arbiter. The argument might appear appealingly up to date. But it is wrong. Wrong in the assumption that the unsubstantiated trash of chat rooms and bulletin boards reaches anything like the audience that traditional media (however embattled) commands. Wrong that a rumour on the internet has sufficient credibility to warrant a denial. And wrong that once a name is "out there" online, it might as well be in print (even electronic print).
Lord McAlpine is a case in point. It is no hypocrisy to name him now. Indeed, he issued a statement himself yesterday, describing the allegations as "wholly false". That the newspaper story also sought to exonerate him is irrelevant. By formally linking his name with the affair – even in denial – it has ensured a taint that will be impossible to remove.
Under the glare of the Leveson Inquiry, newspapers and broadcasters alike are struggling to defend themselves against the accusation that all journalism is tawdry. Phone hacking caused such damage precisely because it blurred the line between good practice and bad. This week's imprudent stunts have blurred the line between good journalism and no journalism at all.
The cliché is to describe the internet as a "Wild West". Rather, it is the mob in full cry – capricious, uncontrollable and hot with rumour. The conspiracy theories and unsubstantiated accusations bandied online are not worthy of notice. Even to deny them is to give them a recognition they do not deserve, more so than ever in such febrile times as these.