The scuba diver voluntarily waives his or her "right" to keep personal medical information personal when they contract for training with a dive agency or for diving with an op. It is the agency's and op's perfect right to ask the diver to be honest with them regarding medical conditions that could mean additional risks to the business, other customers and diver himself. There is nothing illegal, inappropriate or unethical about this. From a legal standpoint, the businesses would be insane not to.
In fact, asking the customer to complete a medical questionnaire is consistent with the guidelines of The Recreational Scuba Training Council (RSTC), a worldwide organization which establishes minimum training standards for recreational scuba in order to promote public safety. PADI, SSI, IDEA, SDI, Y-Scuba and PDIC, amongst others, are members.
A diver's verbal assertions that "I'm capable of monitoring my own medical condition, "I won't sue," "I don't pose a risk to other divers," and the like are both practically and legally meaningless. Even if they weren't meaningless, they wouldn't be binding on the injured or deceased diver's relatives, estate or other entity with legal standing in a negligence or wrongful death suit.
The diver participates in recreational scuba on a voluntary basis. No one forces him to and it's not an activity that is essential to one's livelihood or fundamental well-being. It is a recreation, a past time, a fun thing to do. The individual who does not like the rules or legal maneuvers that the sport uses to protect the diver, other customers and the businesses that offer scuba services, rules and maneuvers like completing medical questionnaires, doesn't have to participate. He or she can find diversions whose rules better suit them, recreations which don't require them to divulge their medical history. Heaven knows there are dozens and dozens of them.
However, if you want to dive then accurately filling out the various forms, questionnaires and waivers required by scuba companies is part of what you must agree to. Lying (and make no mistake about it, it is lying) when completing the medical questionnaire is not an ethical or effective way to address concerns about limiting access to medical information.
Regards,
DocVikingo