Deep Ecology

In their discussion of Arne Naess' concept of "deep ecology", Bill Devall and George Sessions argue that one of the basic principles of deep ecology is that human beings have no right to reduce the richness and diversity of life forms except to fulfill "vital" needs. However, Naess himself claims that deep ecology prohibits humans from destroying the natural features of this planet, and does not mention any possibility of exception(s) to this rule for satisfying our vital needs. Despite this contrast between Naess' and Devall's and Sessions' written versions of this principle of deep ecology, I think the acknowledgment of human beings' need to destroy natural resources to a certain extent in order to survive is meant to be implied in Naess' article. Obviously, human beings need to destroy natural features of this planet to some extent in order to survive (e.g., destroying living things for nourishment), and thus cannot comply with this particular principle according to a literal interpretation of it.
I find that an inadequacy in this principle lies in the fact that neither Naess nor Devall and Sessions go further after revealing this principle as an aspect of deep ecology to explain exactly what constitutes "vital" human needs, or those needs which could be justifiably fulfilled despite their potential negative impact on the environment. Clearly the needs for water, food, and shelter must be included in the category of vital human needs, but where is the line drawn here? Would Naess, Devall and Sessions consider testing new vaccines and other medications on animals before administering them to human beings if this could help us find a cure for terminal illnesses such as AIDS and thus allow many human beings to survive when they otherwise would not? Would they consider our need to prevent the spread of disease vital, or even a need at all? Naess, Devall, and Sessions point out that the term "vital needs" is left deliberately vague in their accounts of deep ecology in order to remain flexible and adaptable to varying judgments. However, I feel that it is important for the sake of their arguments to more clearly define what they mean by "vital needs" so that it is apparent to the reader what anthropogenic environmental destruction they believe can be justified by human necessities.