If I understand it correctly from the many debates here and elsewhere, the reason for the above is a general [what I would call ideological] commitment against the idea of resource exhaustion. The same reason why discussion of human population impact also meets with a hostile response.
I think the commitment arises from two lines of thought: one, that accepting that resources are limited permits imposing draconian measures of control and apportioning which inevitably further deprives the underprivileged; second, that resource exhaustion is not a "real" (pragmatic) issue of concern and is only a theoretical truth, a limiting case.
Assuming my understanding to be correct, I think both lines of thought are worthy of consideration, the second more than the first. I think there are strong counter-arguments against this position (for instance, one could argue that it is the opposite position of infinite resources that affect the underprivileged disproportionately, such as increase in the rates of cancer due to toxic waste created by mass manufacturing).
--ravi
P.S: I think some of you are bothered by words like "underprivileged" but any substitute I can think of ("disadvantaged", "powerless", etc) would probably not satisfy you, either. Instead, I appeal to you to mentally substitute these words with what you would consider appropriate terms.
-- Support something better than yourself: ;-) PeTA: http://www.peta.org/ GreenPeace: http://www.greenpeace.org/ If you have nothing better to do: http://platosbeard.org/