No pilot hate intended. I don't imagine there's a soul here who does. I'm not qualified to address any of your four questions, other than to suggest that once we have the relevant certifications it's up to us to ensure that in addition to the regulatory papers, we also have the mindset, character and professional approach to follow our training and stay within the limits of our abilities and certifications, and are able to assess risks for both ourselves and those others who entrust their lives to us. One need only watch Mayday on the Discovery Channel to see examples of certified, trained pilots, both commercial and private skipping check lists, breaking protocol, making assumptions, flying VFR into IMC, etc.... and getting themselves and others needlessly killed.
I ride a motorcycle, for 20 years now. I am professionally trained, and have partaken in further training courses to ensure I know what I am doing. In my 20 years of riding I have never had an oh sh#t moment, because I am careful, predictable and stick to, and build upon my training. But with all that, I have never, not once, ever taken someone else my on bike. This is my life to risk, not yours. Of course that doesn't mean I won't pack the minivan with kids to head to the mall, needs must. If I was a pilot, I think I would also take my friends and family up. Since, as you suggest what's the point otherwise?
We do not know yet what happened in Nashville, and may never know, and the replies above remind me to check my own assumptions at the door. The preliminary report is inconclusive, yet does list the fuel selector as you mention. I do hope that the possibility of a fuel selector issue serves as a reminder to pilots and those who train them to ensure that whatever can be done to prepare for final landing approach, such as checklists, sterile cockpit rules, etc. are done. If we do whatever we can to remove pilot error, we need only worry about mechanical/system failure.