It might surprise you to hear that I'm not an idiot. Interestingly enough, I'm university educated, am 56 years of age and have three adult sons. Having been instructing diving recreationally and commercially for the past 37 years, I have some idea about learning retention.
I have not once questioned your qualifications, intelligence or education. It might surprise you to remove the chip from your shoulder and read what I wrote. With your university education I'm sure you've opened one or two peer-reviewed journals and noted that highly educated people can have vociferous, even hostile disagreements with each other without once contending that the disagreement is based on intelligence, training, competency or anything other than matters of interpretation of available information.
I also know what is a reasonable question to ask as a new diver and when I answer it and get a "Oh, my Instructor didn't cover that," I have to wonder.
Why? Similar responses are very common among people who have failed to retain information. Most people both over-estimate their own competence and deflect responsibility.
Especially if this happens over and over again. It doesn't matter if in-fact the Instructor did or didn't cover it; it's the Instructor's job to teach and for the student to have demonstrable skills and knowledge. Some of these divers came to me the next weekend after certification.
I have not disputed the existence of poor instructors. Nor have I defended the rise of a certification industry that rests on top of the diving world. In fact I've been critical of said industry because it encourages and rewards the skirting of standards. But that is not an indictment of the standards per se, and can not be used as a blanket condemnation of training as a whole unless you can demonstrate that what you're seeing is normative.
It would be interesting to know how many of those you deem incompetent to your liking are infrequent divers relatively removed from their training compared to those who are newly trained. It would also be interesting to know something about the geographic regions they come from, and even the specific shops. Lastly it would be interest to know how many instructors with significant experience likewise feel that said divers are inadequately skilled. Of course, such data is likely not available, and thus we are relying on anecdotal evidence. And as the old saw goes, the plural of anecdote is not data.
Having been an Instructor with five organizations, I fully understand what many of the standards say. Some of these are in-fact insufficient in my opinion, but that is another issue. When divers are newly certified and don't have a clue, it's not brain surgery to realize that they need more training. I would hope that any experienced Instructor would be quick to pick this up.
It's also not brain surgery to realize that it is very possible for students to pass relatively stringent performance requirements and then quickly loose those abilities. That is what gave rise to the concept of just-in-time training. Even a short break between demonstration of skills and their actual use can significantly effect retention. And that is a phenomenon that increases with age. Since the diver population is getting older, it is not unexpected to see that manifesting itself.
But we ultimately come back to this: what is the level of risk the participants and industry is capable of bearing?
If I wouldn't let them out of the pool, what's motivating these Instructors to do so. Ah yes, the certification machine... Not all Instructors succumb to this, but the ones that think a C-card is a "learners permit without firm deliverables" tend to be more, well lets just say "forgiving."
I would suggest, though only through my own anecdotal observation, that this is far more common in two categories of shops, not instructors:
* those businesses who have single contact with divers -- primarily resorts and cruise ships
* those dive shops who have very little local diving and thus very little revenue from equipment sales, additional training, and servicing of gear.
Certainly instructors are the one's signing the cards. But the reality is that for the most part they wouldn't be instructing without the shop support, so it is the shop, not the instructor setting the rules. And for those instructors who are also the shop owners, cognitive dissonance tends to resolve in the direction of self interest.
I am not in disagreement with you that there are a lot of bad instructors out there. Nor am I in disagreement that there are divers who's skills leave something to be desired.
Where I disagree with you is that those insufficiency at the rates they occur now are cause for real concern across the diving community as a whole. The available accident data that I've seen strongly suggests that this simply isn't the case in terms of relative risk compared to many other activities where training is required or at least strongly suggested.
You got me there. Something went terribly wrong on the certification end of things there!!! 
