Trayvon Martin smiles at the camera, a neat boy with nice teeth, wearing a red Hollister T-shirt, 17 and black, who looks, says President Obama, like a son he might have had. Martin will be forever young, globally famous, though for something he would not have chosen. He went out to buy an iced tea and sweets from a convenience store in Florida and was shot dead by 28-year-old George Zimmerman, a large Hispanic/white volunteer with a neighbourhood watch.

Zimmerman was not charged because of a pernicious Floridian "Stand your Ground" law which allows citizens to respond with fists and weapons against suspected criminals or attackers.

And so it was that another framed picture was hung up the vast gallery of African-American men gone before their time, some murdered by white racists or brought down by law officers, others by their own in dystopian badlands controlled by gangs. Such deaths are usually only numbers, a score. This time though, the number became a name, a name we shall not be allowed to forget.

African-Americans have taken to the streets across the US, men wearing hoodies, unforgiving women holding banners, civil rights defenders from the NAACP (National Association for the Advancement of Coloured People) and career marchers Al Sharpton and Jesse Jackson – their eyes hazy but still angry. The teenager, they say, was killed simply for "walking while black".

Jackson calls on his nation to wake up, to notice all those African-Americans who are criminalised, and gunned down. Online petitions are on a roll. Trayvon Martin will not go quietly into the night. The protests have been sombre, dignified, morally charged and implacable. Righteous indignation is articulated by black American churches, fiery and potent. The police and Zimmerman have no place to hide. Race and ethnicity are in the volatile mix. Zimmerman is part Latino; the majority of Latinos, as a Duke University study shows, have strong anti-black attitudes. Police bosses who decided not to charge the accused were thought to have been white.

The events leading to the shooting are disputed, but not the basic facts. Youthful Martin was unarmed and doing no harm, yet Zimmerman thought he was a threat and spoke to a police dispatcher who told him to wait and do nothing until the police arrived. The vigilante ignored these instructions, claiming he was attacked first by Martin, claims denied by some witnesses. The heat is up; Florida police chief Bill Lee has gone on swimming leave.

Watching the events unfold, I wonder why we can't galvanise such protests when similar cases happen in the UK? We used to, long, long ago. I wore out many pairs of special demo shoes with padded inner soles. This was back in the 1980s when thousands of us marched on police stations where officers had maltreated black suspects or ignored their unlawful deaths. The last time we saw such massive outrage was when Stephen Lawrence was stabbed to death. That led to a major inquiry.

Now we seem utterly hopeless, reacting with fatalism or with stupendous nihilism. Mark Duggan, mixed race and known to the police, was shot dead last year, triggering riots across England. Rioters soon forgot Duggan, captivated as they were with goods.

Four weeks ago Anthony Grainger, white, and also known to the police, died as a result of an apparently maddened police operation. In both cases the victims had no record of violence yet grossly misleading reports were published stating the men were armed. They weren't. Now an inquest into the Duggan shooting can't go ahead because some evidence is "confidential". No officer has been charged with any wrongdoing thus far. The Grainger family, understandably, has little faith in the inquest.

Meanwhile, last week a black man from London's East End recorded his treatment in a police van, physical assaults and racist abuse. If people were aroused and came out, they would stop such failures of accountability and possibly change behaviours.

I am not suggesting demonstrators should only follow police actions. Black American activists are also targeting Zimmerman's alleged racism. Here, a beautiful five-year-old Asian girl, Thusha Kamaleswaran, who wanted to be a dancer, was shot and paralysed in a relative's shop by black gang members. To date good black folk have not walked the streets to condemn the thugs. They must know small shops owned by Asians are terrorised by such gangsters. And when British Pakistani men are found guilty of organised sexual abuse of white girls, what stops us from marching – to damn what they are and what they do?

There has been much pessimism about the effectiveness of public protests since anti-war marchers were ignored by Bush and Blair and the contemptuous disregard shown by the Coalition towards professionals objecting to their NHS and education policies. But collective street activism is still worth it. At some junctures, it speaks up for virtue and integrity and reminds institutions and leaders and communities too of their responsibilities and ethical conduct. We should learn from the US and rise up more, and more effectively.

y.alibhaibrown@independent.co.uk