A post last week at the Neuroanthropology blog indexed some research into the role of internet communities in reinforcing "delusional" thought patterns.
An interesting question raised by the featured researcher (and blogger), Vaughan Bell, is what criteria must be met to classify a belief as a delusion; if an individual's self-selected culture (e.g., a supportive internet community) validates a particular belief, then marginalizing it as psychopathological would be a failure to maintain the neutrality of an ethnographically etic perspective, let alone the ideal of cultural relativism.
This is a problem as old as anthropology itself. Is it ever the right, or even the moral duty, of a cultural outsider to criticize or intervene in the practices of insiders? This leads directly to questions of universal morality, of which there are as many answers as philosophers, so as one might imagine, consensus has not been forthcoming.