The debate over using supplemental oxygen in extreme-altitude climbing began during the first attempts on Everest in the 1920s. If it were much higher, the summit would likely be unreachable without supplemental oxygen.
Climbers are chronically hypoxic, and they report that the skin of other climbers has a bluish cast.
Although our energy for metabolism comes from food, oxygen is the catalyst for the metabolic process, and its presence determines whether or not we can exert effort. If you turn someone's oxygen off, they stop moving. With oxygen you function better, think more clearly, stay warmer, and are able to climb steadily without pausing every step to suck in six or eight gasping breaths. My personal goal is to see how I can perform, to experience the mountain as it is without reducing it to my level. For me, how I reach the top is more important than whether I do.