There was a moment early in the Olympics when an Italian competitor won a silver medal in shooting, collapsed on the ground and cried like a baby. His body heaved to the jerks of uncontrollable emotion and though one empathised with his heartfelt reaction, it was hard to know what to think. As a metaphor for the 29th Olympiad, it was appropriate.

What, you wonder? Where’s the sense in even a hint of ambivalence? Weren’t these the best Games we’ve seen? Michael Phelps and Usain Bolt and all that. Those Jamaican women and, at last, a stream of British gold medallists; the refreshing Rebecca Adlington, the masterful Chris Hoy, a GB team that performed far better than expected. Was this not the sporting moment for which the country waited?

And, there were other reasons to celebrate Beijing. China’s government invested billions in the infrastructure and the organisation, its people gave heart and soul, warmth and energy. London’s greatest difficulty for 2012 is easily pin-pointed. Nine o’clock in downtown Beijing on Thursday evening and every taxi is occupied, a mother and her young teenage daughter approach. Without a word of English, the mother gently encourages her daughter. The girl speaks English. “Sir,” she says, “if you go down the street, take the first left, it will be easier to find a taxi.” Consider what might happen on Oxford Street in similar circumstances.

Especially in the young Chinese, there is optimism, dynamism, the love of homeland that we once had. They believe in the future. We worry about it. London 2012 will not be easy for Lord Coe and his team. In the terms that the International Olympic Committee judges its showpiece, Beijing was a hugely successful Games. Its biggest sponsor, NBC, paid $894m for the broadcast rights but the US company has already recouped more than $1bn in advertising. The ratings were spectacular. For example, 842m Chinese watched at least one minute’s coverage of the opening ceremony, 500m was the average audience in China for the four-hour opening. Forty-million watched Phelps win his eighth gold medal in the US, more Australians watched the Beijing Games than watched Sydney eight years before and during the height of Team GB’s heroics last week, the BBC’s online coverage of the Games attracted an audience in excess of 1m.

The IOC was also pleased that of the 204 nations taking part, 50 won gold medals and more than 80 won a medal of some sort. Such a spread helps television ratings and is therefore good for business. In India, there were 12m video downloads of shooter Abhinav Bindra winning India’s first individual gold medal. As fans, we’re cheered when smaller nations leave with something to show for their efforts.

As a purely sporting event, 17 days of competition depended to a dangerous degree on the brilliance of Phelps and Bolt. Both are extraordinary athletes and it may be that these Games came at the perfect moment for them. At 22, Bolt will be expected to improve further but who knows how he will cope with injury, fame, success and the difficulty faced by all of those who travel far in a short time - soon they feel they have nowhere left to go.

Certainly Phelps is unlikely to win eight gold medals in London or any Olympics beyond. Beijing gave its medals, and seven world records, but will have taken something in return. Besides, how could Phelps ever again win races as desperately close as the 100m relay and the 100m butterfly? He deserves everything that will now come his way. Bolt and Phelps were out of the ordinary before their time. Phelps set world records at age 15. At that age Bolt became the youngest ever junior world champion. Given the level of suspicion that comes with transcendent performances, there is some reassurance in their respective career paths. From the very beginning, they were frontiers beyond their peers.

Phelps has sought to demonstrate his commitment to racing without drugs by signing up for extra testing with the United States AntiDoping Agency and is part of their Project Believe programme. Bolt comes from a small country with modest resources and Jamaica has yet to set up its own antidoping programme. For whatever reason, it refused to join the Caribbean Regional AntiDoping organisation.

Three years ago, Elliott Almond of the San Jose Mercury News wrote a story that claimed Jamaican and Caribbean athletes in general were being tipped off by customs officials when international drug testers arrived at Kingston airport. At these Olympics, Jamaica’s female sprinters took five of the six medals on offer in the 100m and 200m. It may be that a country of 2.6m can do this through natural talent and excellent back-up. It may not.

For here is the territory of ambivalence, where honesty leads to suspicion and suspicion takes you to the edge of disaffection. Ninety-one-thousand people filled the Bird’s Nest last evening and coalesced to produce an atmosphere we haven’t often seen at these Olympics. If we cannot trust what we see in this arena, and we can’t, the show is diminished. Not many of you will see it this way because television, having paid big money for the rights to broadcast, tells the story in a way that serves its commercial needs.

Had you watched the televised final of the women’s 400m hurdles in Athens four years ago, you would have seen Fani Halkia winning a gold medal for the host country without being told her rise from nowhere didn’t make sense. She was that evening’s heroine. Earlier this month it was announced that she had failed an out-of-competition drug test and we were spared her presence at these Olympics. Almost 50 others were caught in preOlympic testing but many dopers still slip through the net.

What do you say when Britain’s heptathlete Kelly Sotherton and long jumper Jade Johnson complain in Beijing that they are competing against cheats? They come off the track convinced they didn't get fair play - we can ignore them just as easily as we can ignore reality. Last Tuesday evening, Christine Ohuruogu was television’s girl, Team GB’s only gold medallist on the track. Away from the cameras, her postrace press conference was a sparsely attended and joyless event. “Last question,” said the Chinese host. Nobody was bothered. Ohuruogu’s only mistake may have been forgetfulness but in this poisoned world, it is easier to win a gold medal than to receive the benefit of the doubt.

Three days ago, the New York Times’ track and field writer Jere Longman wrote the following: “Personally, I would allow athletes to put what they want into their bodies. At least sports would be more honest. Let’s have the Winstrol 200 and the Stanozol 400. I have no ethical opposition to performing-enhancing drugs. I just want to be able to trust what I’m seeing. Right now, that is not possible.”

The Olympic playing field is changing but perhaps not for the better. With all its glamour and feelgood stories, television’s Olympics become the only Olympics. Those who care about the right of each athlete to start on the same line as all of his or her rivals are losing or have already lost. Soon sports administrators will tell us the war against doping is being won. Then, you will know it is business as usual in the performance-enhancing factory.

And what of Britain’s multitude of medallists: are they to be trusted? Based on their performances, the sports in which they compete, the environments in which they prepare and the testing to which they are subjected, most if not all probably are clean. It is not coincidental that Britain struggled in the sport where doping remains a significant problem, athletics.

With UK Sport wanting gold in return for the money it dispenses to various sporting bodies, it is likely that track and field athletes will have their funding reduced or cut off. It will be a mistake because athletics is a sport that must be promoted. There is a bigger picture than the one that gripped a nation over the past 17 days and if the successes of these Olympics do not inspire more young people to commit in some way to sport, they will not have served their ultimate purpose.

Why would a country spend millions on its elite athletes if not to encourage sport for all? Arsène Wenger was right to wonder the other day how the GB team could deliver so many gold medals to a country where sports facilities are substandard and in many areas nonexistent. For most young people, athletics is a far more accessible sport than sailing, rowing, swimming and track cycling. In the mad rush for medals, that is something to remember. Lessons for London: David Walsh on what the capital can learn from the Beijing Olympic experience