It isn't possible for modern anthropologists to passively collect information or record a culture. They are often placed in such diverse roles as advocates, activists, policy designers and advisors, that can have profound political and academic ramifications. Often, their research is applied research, funded by governments, businesses, or agencies with a financial or vested interest in the outcome.
The American Anthropologist Association's states that " In research, anthropologists' paramount responsibility is to those they study. When there is a conflict of interest, these individuals must come first. Anthropologists must do everything in their power to protect the physical, social, and psychological welfare and to honor the dignity and privacy of those studied. a. Where research involves the acquisition of material and information transferred on the assumption of trust between persons, it is axiomatic that the rights, interests, and sensitivities of those studied must be safeguarded."
(For the American Anthropologist Association's complete Statement on Ethics see their webpage at http://www.aaanet.org/ethstmnt.htm.)
The problem then, is what exactly are the rights and interests of the Yanomami.
Cultural relativism is a term coined by pioneering anthropologist Franz Boaz in the early part of this century, meaning, basically, that cultures evolve relative to the demands of their environment. Cultural evolution, like biological evolution, is not linear. There are not "higher" or superior cultures.
Most anthropologists adhere to at least part of this perspective. They are also among the quickest scientists to admit that their own cultural biases enter into their study and interpretations of another culture, no matter how objective they try to be. Sometimes an action that seems to be in the best interest of the study group may simply be an extension of the anthropologist's cultural perspective and is actually disregardful of the subjects. Instead of protecting the psychological welfare of those studied, they impose their own cultural biases and protect our own. Other groups are even more susceptible to this cultural bias and projections.