An important part of safety engineering is to understand that people will make mistakes, become complacent, get distracted and not pay attention, etc. Safety is about ensuring those things don't lead to catastrophe. An example I was peripherally involved with:
A technician working on equipment attached to airframes was supposed to use new bolts when re-attaching the equipment but, because there was an issue with supply, he started re-using old bolts. He perceived that "a bolt was a bolt", while failing to complete the work on schedule resulted in negative customer feedback and an unhappy manager. Fortunately the company had an auditing system, which quickly flagged the problem. A gap in the training system was identified, and a deficiency in the safety culture of the workplace was revealed. Training happened; no-one lost their job; and the result was a better, safer, and happier company.
Solo diving to 90 m using equipment and gasses outside of accepted best practice seem to me to be fundamentally at odds with safety. On the other hand, I personally believe that people should be allowed to take risks, so long as they had the proper training to understand those risks, and they aren't endangering other people, who hadn't signed up for the risk. Again, as a personal thing, I stopped taking those risks once I had kids.
Maybe recreational divers need to acknowledge that there are some parts of the sport that fall outside of safe practise, and there are things they do that simply wouldn't be acceptable in commercial or military diving.
