Truth is, mental fitness trumps all. It's not PC to say that stupid people shouldn't dive, but considering how many people dive beyond their skills and knowledge or profess knowledge based on anecdotal evidence, maybe we SHOULD limit diving to people with a minimum set of standards of mental fitness. Let's put an IQ minimum on people, let's have mental evaulations. But of course that's not a popular position to stand on.
Fat and smoke have anecdotal evidence. Stupidity and panic have more documented incidents.
Smoking and obesity have NOTHING on diving with people who have a tendency to panic, have poor decision making skills, are emotionally troubled, or are just plain morons. I'd take a fat diver who dives in their limits over an moron any day.
For the third or fourth time, I'll point out that this discussion isn't about dive safety.