I honestly don't have any problem with people making their own decisions about what degree of risk they are willing to take to do something, so long as it is an EDUCATED decision. Most people with asthma think, "Well, if I can breathe okay, I should be able to dive!" They don't know enough to know that even asymptomatic air trapping in the lungs can be lethal. We lost an experienced cave diver in a mine a year or so ago, because he had a tumor in his lung he didn't know about, and it created an air-trapping situation that resulted in AGE and death. You don't have to be significantly short of breath to have air-trapping.
If someone KNOWS that's the risk, and decides to dive anyway, I think that should be their right. But when they go to a doctor and ask for "clearance" to dive, that doctor becomes liable for anything that happens to them as a result of the condition they described when they went in. In our liability-happy society, when you die because you decided you wanted to dive enough to take the risk to do it, the doctor is the one your wife sues, because she goes to an attorney who says the doctor has malpractice insurance and thus deep pockets. This is why doctors are so incredibly risk-averse, and so reluctant to give someone the go-ahead to do something that involves a recognized risk.
As long as shops and agencies require medical clearance, and doctors are liable for the results of that clearance, then the error will ALWAYS be made in the direction of refusing permission rather than taking a chance.