I'm not sure your examples to date are relevent to the type of diving most people can relate to. Of the three examples I've seen so far, one guy went to 275 feet while still uncertified, one went shallow but apparently didn't know how to equalize and hurt himself, and this guy jumped off a boat in lead boots apparently without the benefit of a breathing apparatus. Did he really expect not to sink and drown?
These are not really learning experiences, as most people aren't dumb enough to do them ... and one could reasonably expect death or injury to be the likely outcome.
Your premise in the first two examples was "don't try to teach unless you're an instructor". I'd say that premise has merit in most cases ... but the fact is that a lot of people can and do learn an awful lot about diving from more experienced divers who are not instructors. It's more a matter of using good judgment about what you should and shouldn't attempt to do.
Your premise in this thread is "don't dive without a buddy" ... but it's dubious at best that a buddy would've made any difference in this case. I'd say a better premise is "don't jump off a boat in lead boots unless you're attached to something you can breathe from". Otherwise, drowning is pretty much an inevitable consequence.
In both cases, I think the moral of the story should be that diving is as much about making good decisions as it is about following rules of thumb that are generally intended to help reduce the risk potential of diving, but are not a panacea in all cases. Like all rules of thumb, they apply more in some cases than in others ... and the trick is learning how to discern when to use them and when they're not really going to be all that useful.
I don't think people are trying to be mean ... they're just looking for some sense of why you're posting these stories. Take some time, and build up your credibility as a contributor. If you're asking for advice, I'd say poke around the forums a bit and use your experiences to add context to some existing threads before trying to initiate topics that purport to tell people what to do ... there's a whole world of different perspectives in here, and we rarely agree on anything. Learn how to contribute, and whose opinion is worth taking seriously. I think I was on ScubaBoard a good month before I started a thread ... and that was more than 11 years ago when it was a much more close-knit community.
And welcome to ScubaBoard ... it can be a bit daunting at first ... but it grows on ya ...
... Bob (Grateful Diver)