Simon Barnes is blogging from Beijing every day. Follow his Games here

The worst decision sport ever made was to start testing for drugs. Once they began to catch the cheats, all hell broke out and we began to lose the faith. In particular, we began to lose faith in the core Olympic sports of athletics and swimming. Now the world is full of people declaring that they don't care who wins what at the Olympic Games, because “they're all on something”.

When the Games come, many of these doubters will watch anyway, because the Olympic Games are a bit un-look-away-able. But for how much longer? The credibility gap is growing, and it grows, not when a cheat gets away with it, but every time a cheat gets nabbed. Every time the anti-doping forces do their job, the sport moves a little nearer death. Every time a cheat is missed, it's a small reprieve.

But it's only a few cynics arguing a line for the sake of it who say that testing should be scrapped and may the best pharmacist win. People who actually like watching sport - the people who actually matter in any professional sport - are mostly agreed that doping is a bad thing and that people who dope should be banned.

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No one is quite sure why. Is it because doping is immoral? Or is it because doping is dangerous to the user? Normally, someone who knowingly does something dangerous in order to achieve great things is regarded as a bit of a hero, even if the task in question is comparatively pointless, like climbing Everest or sailing single-handed round the world. So isn't someone who knowingly takes a dangerous drug to win a gold medal for his country also a hero?

Well, the consensus replies with a big no, perhaps in the flawed belief that the clean athlete is doing it for his country while the cheat is doing it for himself. But the irrational response is very strong: perhaps distaste - even physical squeamishness - is as much the reason for the war on drugs as any lofty notions of morality. The squeamishness comes first, the morality second.

There is a sense in which drugging - altering your body - for the sake of mere sport makes sport too important. Sport, for those who watch, is just a pastime, an entertainment, we don't want it to be a life-and-death matter. There is also the argument that the troubled sports must stop doping because people will stop their children doing them.

The only certainty about doping is that people don't want it. The World Anti-Doping Agency (Wada), is committed to eliminating EPO (erythropoietin) - and there are more than 50 types to eliminate - even though it is not dangerous. And then there is all the stuff that lies ahead at genetic level. Is it immoral to select genes scientifically, rather than by the natural lottery? Is it immoral to work on embryos in vitro to produce a master race? Wada is looking hard for the moment when such talk becomes sporting reality.

As I listened to the high-ups of Wada explaining their standpoint yesterday, and their belief that they are “getting smarter”, that the arms race between testers and the tested is going the way they want, there was still an air of moral confusion. We don't know why it's wrong, but wrong it most certainly is. It's something to do with the purity of sport.

And I was reminded of the last great moral debate at the Olympic Games, another great problem, full of cheats and dodgers and scandals and people getting caught and people getting punished and banned and vilified for ever more. It was about professionalism. We laugh at the debate now: ha ha ha! Fancy banning a man for making a few quid from sport!

But it was an issue that raised the passions and broke the hearts, one that had its victims and its defiant, knowing cheats and liars. An Olympics without amateurism was unthinkable: now an Olympics without professionalism is equally unthinkable.

An Olympics with drugs is unacceptable, but will that too change in a changing society? And as the issue of genetic manipulation becomes increasingly relevant, who, apart from a religious fundamentalist, knows what we should think?