Environmentalists pay attention to the high cost of protecting endangered animals and propose that we should decide which animals to be protected by evaluating the value of various endangered animals to human beings. This method is not practical, because it is impossible to predict the future value of an animal. It is also impossible to evaluate the value of animals that make indirect but important contributions to human beings today.
The main argument of the above is that it is impossible to assess whether endangered animals are important to humans.