We are not talking about refusing to answer questions based upon some legal, practical, or ethical principle. Obviously you are free to decline to answer any questions.
We are talking about knowingly lying on a form, and signing your name affirming that you have told the truth.
Different thing.
No, we're talking about the equivalent of checking the "i agree" button on a EULA license on a software package. It is a non-negotiable undue burden that is imposed by the dive operator as a requirement to use the product/service.
Where they willing to accept a note from my doctor stating that I had a complete dive physical and am cleared to dive, without revealing any specific medical information for which they have no need, no expertise to evaluate, and provide no guarantee of confidentiality, then there would be no issue as I, and I'm sure everyone else who state saying "No" is just the best solution, are not interested in diving unsafely when we should not. We're interested in protecting privacy.
Given the ubiquity of these documents, and the non-negotiable stance the operators take with regard to having the forms filled out, simply telling them what they want to hear is the only reasonable recourse those who know they are medically cleared to dive and care about the privacy of their medical information have.
It is not a moral question. To call it "lying" makes a value judgment that is simply not applicable. We're clicking the button required to start the service.
From the perspective of a (former) small business owner, I can't help but think that the dive operators would rather see divers with physicals and expert evaluation of their fitness to dive checking "no" when that is not the case than divers with undiagnosed conditions checking "no" out of ignorance. And I'm fairly certain that the latter is far more common than the former.
Requiring a dive physical would be a far better solution than this questionnaire, which is nothing more than an unnecessary and burdensome point of contention applied in an ignorant attempt to limit liability without due concern to the interests of the customer.