The full paragraph that you're quoting from was the following:
"First, as a matter of physiology, there is a HUGE difference between, on the one hand, living and training at an altitude of, for example, 6,000-7,000 feet (typical for many Kenyan and Ethiopian runners) and, on the other hand, spending eight to twelve hours a day breathing gas that (whether by increasing nitrogen, decreasing oxygen, or lowering pressure) simulates oxygen transport conditions typically found at 12,000 to 13,000 feet altitude while continuing to train under conditions in which oxygen is much more readily transported. Laboratory experiments have generally shown very little, if any, increased EPO production or increased red blood cell mass in moving from sea level to moderate (6,000 to 7,000 feet) altitude, although the concentration of red blood cells will typically increase because of a decrease in total blood plasma volume. Breathing gasses with lower oxygen concentrations for eight to twelve hours a day, however, will cause significant increases in endogenous EPO production and red blood cell mass, without a corresponding drop in blood plasma volume and without requiring a reduction in training intensity. The use of so-called "altitude tents" is, physiologically, much more similar to blood-doping by autologous red blood cell reinfusion or exogenous EPO injection than it is to living and training at moderately high altitude."
After I posted that paragraph, I realized that someone might, as you perhaps did, read the sentence "Breathing gasses with lower oxygen concentrations . . . " as a reference to breathing gasses with any lower oxygen concentrations whatsoever, rather than breathing gasses with the lower oxygen concentrations typically found at 12,000 to 13,000 feet altitude, as I had stated two sentences earlier. As I indicated in that same paragraph, the evidence of increased EPO production or increased red blood cell mass in moving from sea level to moderate (6,000 to 7,000 feet) altitude is equivocal at best. With that clarification, I don't know whether you still object to anything that I said.
I was curious about your pseudonym, "secret cheater," which perhaps suggests that you use an altitude tent yourself. I want to be very clear that I don't regard the use of altitude tents as cheating in the absence of a rule that prohibits their use. I feel the same way about many types of alleged performance-enhancing practices, from carbohydrate loading to caffeine loading to autologous blood-doping to the use of anabolic steroids. Although the rules governing prohibited performance-enhancing practices were very nebulous forty or fifty years ago (which was why there were serious discussions back then about whether running long distances in training to "burn off flesh" violated the rules of fair play governing Olympic marathoners), the rules have evolved over time from general prohibitions on "unfair" practices to a collection of rather specific bans, with the unstated implication that practices not specifically banned are generally permitted. I think that's a good thing. But it remains an open question as to whether the use of altitude tents should be added to the list of banned practices. The debates on the subject have generally been very primitive and unenlightening to anyone who tries to think carefully about these matters.
My own views about the subject are mixed, but I am definitely less impressed by performances that have been achieved with the assistance of altitude tents than I am by otherwise identical performances achieved without their assistance, and I am concerned about seeing the sport of distance running move further toward a dependence on technological advantages. I happened to be watching the movie "Endurance" over the weekend, and was once again struck by what a wonderful sport this is, where a dirt-poor farmer's son from Ethiopia can compete head-to-head with almost unimaginably wealthy and technologically-advantaged people from places like the United States. Although scientific and technological knowledge cannot be unlearned and expunged from this sport, I would like to see the sport retain its fundamental simplicity and universality.