The age at which a person should be able to dive (and under what circumstances) should be data driven. Can we demonstrate that they are at greater risk? Can they be expected to act responsibly--and under what degree of stress? Until we have a more data and a more complete understanding, we should still be able to have a civil conversation with people whose experience and/or risk tolerance differs from our own.
The problem is that we have become a society where any injury/death is intolerable. There are risks to everything we do. We know for a fact that driving is the most likely cause of death to those under 25 (I do not remember the specific age but it is youth/young adult). We know that this rate is very high. Do we not allow them to drive because of this? Why is it acceptable in this case but not in others?
Your statement is spot on when you said "people whose experience and/or risk tolerance differs from our own". When I grew up, parents would often say "go play in the street"... so I did. The concept of danger/risk was much different. We are moving to a point where risk is not acceptable in any circumstance. That is driving us to the 'nanny state', which is a term I have now used only a handful of times but it applies. Why, when there are different experiences/risk tolerance, is it not up to the parents/children relation to determine what is acceptable? When you say 'I also don't care what parents think about vaccines', I can say I have picked up my child from her high chair limp, unconscious and not breathing after a vaccine incident. We, with the doctors, believed that it was one of them specifically. She did not get the booster for it until later in life. Can it be proven, no but it was known to the doctor that his has happened to others. All medications have risks, typically including death.
Parents absolutely need a role in what is allowable for their children. Diving has been a part of my life since I was young, and it became a part of my daughters. What is right for your child, or Ken's if he has one, is not necessarily right for mine. He may not agree with 10 being the age of Jr OW but without excessive injury/loss, he has no stature in overriding my decision to have my daughter dive. If he does not like it, do not teach youth, do not allow his children to dive etc, but DO NOT TELL ME mine should not. Diving since the early 80's at least, has been 12 for full open water or the later implementation of Jr OW at 10-15. The difference was that when I learned in the 80's, I was cave diving, I was deep diving and other 'harder' dives without parental guidance or support. At least the Jr OW requires a parent until 15. Now I can guide my child's development.
As for your comment 'Can they be expected to act responsibly--and under what degree of stress' - Sorry I have seen adults fail this and children pass. Nobody will know how they will react until put under stress.
Overall, I think that we see very few incidents for child diver injury/death when we look at all of the incidents that are reported here. We need to be aware of the tendencies to limit accountability and exposure for the sake of perceived safety when the risks are acceptable to those involved.