Agreed. Over the ocean auto descent after pressurisation failure might be useful but in busy European & US skies a plummet without some sort of ATC clearance could lead to more serious consequences. A mid-air would clearly be more hazardous than temporary hypoxia for some passengers.
I'll have to disagree. A study done some years ago concluded that, strictly from a statistical point of view, mid-air collisions would occur at a lower rate if pilots flew at random altitudes and directions completely uncontrolled. In other words, the sky is a big place.
Yes, a midair will ruin your day, no argument there. But if you turn off course, it's so freakishly unlikely that it's hardly worth considering. Can anyone reference a single midair resulting from an airline pilot doing what he felt was necessary during a serious emergency?
In an airliner suffering decompression, if you do everything correctly, the pilots are still in serious danger as long as they are at an altitude above which they can operate without supplemental oxygen. If it were me, I'd be on my way to a lower altitude immediately.
Waiting for ATC clearance during ANY very serious emergency was NOT in my bag of tricks back when I was flying over the North Atlantic and Europe. I suspect more people have died by turning control of their aircraft over to ATC than have died by doing what was necessary during a genuine emergency and then telling ATC about it later.