This explanation might possibly help the oxygen debate:
"At 10,000 ft the partial pressure of the oxygen in the lung reaches 80 mbs. This is the minimum that a healthy person can tolerate and accordingly, above this height, the first symptoms of lack of oxygen, or hypoxia, appear. Between 10,000 and 15,000 ft the ability to perform skilled tasks such as aircraft control and navigation are impaired while between 15,000 and 20,000 ft there is a marked deterioration of performance, even of simple tasks, together with a loss of critical judgment and willpower. Thinking is slowed while muscular incoordination and clumsiness result. Above 20,000 ft the symptoms become severe, rapidly leading to unconsciousness.
The onset of hypoxia can be delayed by increasing the proportion of oxygen in the inspired air with the result that the partial pressure of oxygen in the lung is increased. Assuming that the pilot is breathing 100% oxygen, then the partial pressure of oxygen in his lungs will not fall below 130 mbs until above 34,000 ft. Above this altitude, even when breathing 100% oxygen, the partial pressure of oxygen in the lung will reduce, and breathing 100% oxygen at a height of 40,000 ft is equivalent to breathing air at 10,000 ft. Above 40,000 ft, hypoxia can only be prevented by employing pressure breathing."