People that climb Everest know that they are extremely vunerable to the weather, accidents and medical complications. They also know that it is literally IMPOSSIBLE to plan for the worst case scenario and get somebody out alive. Hell some of the bodies are still up there.
However, in diving, it IS generally possible to carry enough gas to get a pair of divers out of trouble. If they plan for it as a team, it is feasible. That is a very big distinction.
Now if you are talking about crazy, solo, penetrations in deep wrecks on air with no guidline.... I totally can understand that that kind of dive is better done solo....
However, the letter was not written for those types of people. It has to be directed toward the "normal" tech diver student ( I assume)..
I've never shared air with someone at 200 feet, but i would not dive with someone in 200 feet if I thought that it would be impossible to accomplish the task. If a buddy is incapable of rendering assitance, then you are far better off being alone on a dive.
Dumpster Diver.
The vast majority of Human Beings who climb Everest do so on Gas. The reason for doing so is that you are operating at 1/3 of the available oxygen content as compared to sea level. Above 26 thousand feet you are in The Death Zone. It is a place that the body CANNOT survive for extended periods of time. Your cells are dying. Read a book entitled Death Zone: above 26000 feet.
Many who die on Everest do so due to Oedemic incidents and the fact that the body CANNOT survive at that altitude. Calorific intake is 1/3 of that at sea level. You struggle to eat therefore your body devours is reserve food stores. Yet others die of Hypothermia. Some fall. Some are crushed in Serac collapses on the ice field or are killed in Crevasses.
How can you dive to below 200 fsw and not know that existing medical conditions, accidents, hypothermic incidents etc not be a possible source of Death?
You are in an Extreme environment, just as you are above 26000 feet, you require your equipment to keep you alive and your mental stamina to drive you on, be that to accomplish your goal or accomplish a successful retreat. Hopefully a Buddy can help you but if they are also in the same state then neither of you are having a good day.
There is a point on Everest that Climbers have been left to die. You read about, maybe are sad about it. That is the reality of the endeavour mate. It is a reality of Climbing to the extremes. It is also a reality of EXTREME level dives. You read about it, maybe are sad about it but what do you really LEARN from it?
There is a story of a successful rescue from 27000 feet on Everest. 2 of the rescuers died. Extremely accomplished climbers. They were Climbers with families. Both got killed due to exhaustion and succumbing to the effects of AS (after they gave the dying climber their gas) due to over exertion from trying to save a guy who was clinging to life by the barest thread.
The guy in question lost an arm, all his toes and fingers on his remaining hand and most of his nose and lips to frost bite.
Two families that could have had Husbands and Fathers at home, had they not done what they did and given up their Gas to keep him Oxygenated and slaved away to get him down thus dying of Oedemas, could have lived fuller lives.
Your comparison of the Extreme conditions on the worlds highest peak and ultra hardcore diving are not thought through. Your experience as a Diver dwarfs mine. I admit that, yet don't patronize me about safety margins after I have seen Men and Women Die climbing. My thought processes which I apply to Hardcore Climbing apply to Diving. IF I CAN HELP YOU I WILL AND I WILL MOVE HEAVEN AND EARTH TO BRING YOU HOME TO THE PEOPLE WHO LOVE YOU, I IF I CAN REASONABLY ENSURE MY SAFETY. I ALSO HAVE A WOMAN WHO LOVES ME TOO AND WANT TO GO HOME TO HER AT THE END OF THE DAY. IF NOT, YOU ARE ON YOUR OWN.