If you want to see a world that takes equality seriously, then come to Los Angeles this week for the Special Olympics World Games which run through Saturday at stadiums, ball fields, tracks and pools around the city.

Take a seat in the stands and root for your country, or your common humanity.

The athletes, about 6,500 from 165 countries, are all amateurs, but their intensity runs hot; the competition is not taken lightly. I watched qualifying track-and-field races on Saturday at the University of Southern California. In smothering heat, young women threw all they had onto the 400m course, some crumpling at the finish line. I squinted to follow one young runner at a distant turn, trailing and alone. She had no choice but to brave it out - or give up, which she did not do.

Bravery is a core word in the Special Olympics movement, embedded in its athletes' oath, which concludes: "If I cannot win, let me be brave in the attempt." Brave these athletes have to be, to rise in societies that tear them down.

The competition, started in 1968 by Eunice Kennedy Shriver, has grown into a global movement, an informal tribe whose membership - those with autism, Down syndrome, learning disabilities, fragile X syndrome and other conditions - transcends all boundaries. Whatever country or class they are born into, people with intellectual disabilities are frequently humiliated, abused and ignored.

A member of the Botswana delegation told me that children with intellectual disabilities are often seen in that country as a source of family shame, taught in segregated schools, kept at home or sent away to the empty countryside, where the cattle are kept. Much the same thing happens in other countries, even in the developed world, where it is called institutionalisation.

When Special Olympics officials say their athletes are the world's most vulnerable and neglected population, they mean it literally.

Special Olympics have become a global public-health organisation simply because their athletes kept showing up with serious, untreated medical problems. At the first health clinic at the World Games in 1995, 15 per cent of athletes had eye or dental ailments so debilitating they were sent immediately to the emergency room. Almost 20 per cent were in severe pain.

At the 2015 Games, large tents on the University of Southern California campus are packed with athletes waiting for check-ups with volunteer doctors and technicians. Along with medals, they will go home with prescription eyeglasses, hearing aids and shoes that fit.

There is a paradox within the Special Olympics - the organisation puts a heavy emphasis on inspiration and joy. It lays that part on thick; it is hard to think of a happier bunch of people.

But its message resonates so powerfully because of the pain it is working to erase.

At the opening ceremony at the Los Angeles Memorial Coliseum on Saturday, 62,000 people roared for the athletes, from Afghanistan to Zimbabwe, marching in native costumes. President Barack Obama greeted them by video, and First Lady Michelle Obama, in person, declared the Games open. Dancers waved ribbons, fireworks erupted and the Olympic torch blazed.

Taking the stage, Special Olympics chairman Timothy Shriver shouted a call to revolution for rights and dignity. "Storm the castle," he roared, not militantly. He meant with basketballs and barbells, roller skates and gym shoes. At a time when other marginalised groups are seeing progress towards greater rights and inclusion, millions with intellectual disabilities are still waiting.

While they wait, they race, run and swim. Los Angeles this week is heaven for a sports fan. I've met a young Irishman who is a champion open-ocean swimmer, and seen young female runners from Africa, some racing in bare feet, some in hijab. I saw a Swedish handball player make an impossible lumbering drive to the goal that won a game in the final seconds.

The Chinese basketball team got thumped by ball-stealing, hard-fouling, high-fiving competitors. Skaters from India raced in slick blue gear, and on cheap roller skates strapped to their shoes. Iran and Israel will both be competing in the sedate, non-Middle Eastern sport of bocce.

But I'm rooting for the Afghans.

NEW YORK TIMES