I second John's opinion on waivers in Brititsh Law countries. In Canada, we use common law and waivers have extremely limited, if any, value. Hail to the Queen!
Fellow canuck Jett and Walt's opinion on risks vs human activities are very well expressed and I share the same. A columnist wrote a few years a go that our society has become alergic to risk... which is an integral part of any endeavour.
We want people to wear helmets to ride their bikes... more so for motor bikes... instruction manuals are ridiculously overweight... thanks to the 50-page warnings that clutter their intro pages. Who needs an advice like: do not put you wet hands in the 240V outlet if you are barefoot on the ground and if the current is on....
The vast majority of people have common sense and if they dive with a reputable operator who understands what he is doing, they are simply taking a calculated risk with extremely slim chances of injury.
Unfortunately, foolishness and stupidity are very well spread throughout the population and there must be as many stupid divers and there are stupid pilots, skydivers or skiers... Mind you, a diver killed by a shark takes up a lot more media space than a skier killed by a tree... which happened to be in his way...
My $ 0,02
Michel