Environmentalists are concerned about the high cost of protecting endangered animals and suggest that we should determine which species to protect by assessing their value to humans. This is practically impossible because it is impossible to predict an animal's future value. It is impossible to assess the value of animals that make indirect but important contributions to human beings today.
the author's main argument?
Because there are imperfect ways to judge the value of animals to humans, decisions based on them are unreliable