What is interesting is this - in 24 pages of missives not a single case of an uncertified youth being taught, mentored, playing, or unsupervised child being hurt by a non instructor can be found. And yet there are several of us that have admitted to doing this very thing. So either they are so buried in Google you can not find them or the are very very very rare...
Okay, I am persuaded that the reward is worth the risk. Let's go diving.
Seriously, I know enough to know that for a variety of reasons 24 pages of rambling on SB and a Google search are not any sort of statistics on which I would rely. The SB posters who said they have done what Grandpa proposed to do may very well be capable of judging and managing the risk. That doesn't mean Grandpa was. We just don't know. I'll take EFX's anecdote for what it is.