A busy afternoon on London’s District line ended with a half-naked black man being arrested for indecent exposure – but now it’s the passengers who stopped him who could face punishment.

If you stop men from undressing on the Tube, you can be arrested in modern-day London. Of course you should accept that crazy people with their trousers around their ankles scream “fuck off” at you on your way home from work.

On Thursday afternoon, 7 August, at 3.30pm, a man was on a packed tube train between Upton Park and East Ham in London. According to witnesses, he started shouting before pulling down his trousers, wrapping his belt around his neck and exposing his genitals – in the midst of families with children.

Several passengers reacted immediately. One man calmly asked him to get off the train, pointing out that there were children present. The flasher responded by shouting “fuck off” repeatedly, before starting to swing his belt at people.

There was no need to wait to see what he would do next, and four commuters took action. They disarmed him, put him on the floor and carried him out onto the platform at East Ham station. An out-of-uniform police officer was present and arrested the man, who was later compulsorily hospitalised under UK mental health legislation.

Now the British Transport Police have confirmed they are investigating the commuters for possible excessive use of force. According to police, the flasher was “assaulted” during the incident.

While the flasher is portrayed as a man in a “mental health crisis” and receiving treatment, those who stopped him risk ending up in court.

The Willowbrook scandal in New York in the 1970s continues to reverberate and echo around the world. The mentally ill have been given free rein because no one wants to protect the public from them by removing them from the public sphere. They are the victims, but it is society that now suffers.

How many innocent lives could have been saved if they were not allowed to socialise with others in society out of misguided kindness? Suddenly a knife is pulled and a completely random victim is killed. This has become a major problem in many countries. When will ordinary people be protected?

It’s all about getting away. The look says it all.

In American cities, they have become numerous and highly visible. This is one of the things Trump wants to clean up, to the delight of many Americans who have become afraid to go out.

We’ve also seen a lot of murders committed by people with severe mental illness in Norway. We should be cheering for everyday heroes who take action to protect those around them without knowing what the psychotic will come up with in the next erratic moment. Instead, these are the ones who should be arrested. A case like this symbolises so much that has gone wrong in the development of society under the “democracy of goodness”, where everyone has equal value.

This incident adds to the string of violent and unpleasant incidents on the London Underground in recent years. Under Mayor Sadiq Khan, crime on the Tube has more than doubled, while police presence has been greatly reduced.

For many commuters, the message is clear: If you take action to protect fellow passengers, it could be you the police are targeting!