A 30-year-old resident of the US who was born in Bangladesh was beaten up in the Bronx on the day of the Boston Marathon bombings. A group of 3 or 4 men, described by the victim as Hispanic looking, had decided that the bombing was the work of Arabs. They then assumed that the Bangladeshi looked sufficiently Arab and ‘took revenge’. The Bangladeshi man hadn’t even seen the news at that point and had no idea why he was being attacked.

This perilous mixture of criminal stupidity and woeful ignorance has been seen time and time again. Lord knows how many American Sikhs were terrified out of their wits after 9/11 by an American public that thinks a turban is a sign of Islam.

My personal favourite was during the India-Pakistan war of 1965 when an Indian was killed in a supermarket in London. Police initially linked the killing to the conflict on the subcontinent and started a manhunt, trawling through likely suspects in the Pakistani community.

Their suspicions were correct, but also wrong. The murder was indeed someone’s attempt to bring the war to the supermarket shelves of the UK. But the perpetrator was as confused as he was criminal. He was himself Indian but thought his victim was Pakistani.

In this case, crass stupidity was achieved without any assistance from the social media, the invention of which was still far in the future. But in this day and age, we have no need to be individual idiots; with a smart-phone we can be collective clowns.

Now when the police decide to ask for the help of the public in identifying suspects, they know they will need a bank of phones and a small army of officers who will not get distracted or driven to despair by the inevitable chorus of callers who claim a likeness to the Dalai Lama, to Uncle Albert who died 20 years ago and has come back to haunt us, and to that pervert next door who always gets this funny look when my underwear is up on the clothes line.

So when the police in Boston decided to publicize the CCTV pictures of the suspects (one thing they got right among a catalogue of other errors), they predictably got many false leads. One was a woman who thought one of the pictures looked like one Sunil Tripathi, a philosophy student at Brown University who had gone missing.

This became a theory for the would-be sleuths on Twitter and Reddit that was reinforced when a second name was added, one Mike Mulugeta. Now I can’t give you any information about this person because in all likelihood he doesn’t exist.

What happened was that an eavesdropper on a police scanner heard something and promptly extrapolated a mere mention into a positive identification. Someone went back and checked what they heard. It was this: ‘Last name: Mulugeta, M-U-L-U-G-E-T-A, M as in Mike, Mulugeta.’

This name was not, I repeat not, mentioned as a suspect. No matter, a Reddit and re-Tweeting frenzy quickly established The Truth, and Redditors were soon patting themselves on the back for their investigative expertise in cracking a criminal conspiracy. Alas, the conspiracy was their own and Sunil Tripathi has gone back to being a missing student and Mike Mulugeta remains innocent for reasons of non-existence.

Then Moroccan immigrant Salah Eddin Barhoum and his friend Yassine Zaime got a bit mixed up when they went to watch the Boston Marathon. They wanted to run the last section after the registered runners had passed but got off at the wrong stop and ended up at the finishing line with their running gear in their backpacks. They decided to stay and watch, and so their faces were caught on pictures taken just before the bombing.

The social media then tagged Barhoum, and his name was repeated and repeated some more. In a brilliant piece of me-first journalism, the New York Post picked up on this online chatter and put the pictures of the pair on the front page with the headline: ‘Bag men: Feds seek these two pictured at Boston Marathon.’

Barhoum immediately turned himself in to the FBI, who hadn’t in fact got him down as a suspect, and the newspaper printed a hasty retraction. But now his dad’s too scared to go to work and he’s getting hate messages on his FaceBook page.

And how did the police suggest he could protect himself from a social media revelling in vindictiveness ignorance? Restrict access to his FaceBook page.

Social media, the technorati among us claim, were integral to the Arab Spring (which has not been quite the blessing that was once fondly wished). But at the time, social media in Thailand was being used for witch hunts and hate speech that was only fuelling the polarization of Thai society (and which would earn the perpetrators prison sentences in less tolerant societies).

Social media does not spread good ideas for the betterment of mankind. It broadcasts ideas, bad and good, false and true, malicious and benevolent. And ten thousand re-Tweets won’t turn the one into the other.

Then again, on the same day as the Boston Marathon, a wave of bombings across Iraq killed at least 33 people. But that’s just Muslim Arabs killing Muslim Arabs. No need for a media hullabaloo about that. Or social media.