Outwith Alternative Medicine, homophily may limit us in all sorts of ways in terms of depriving ourselves of experiences we may otherwise have enjoyed. I think the main danger of homophily in terms of Alternative Medicine is that people with certain dangerous beliefs (homeopathy can cure Aids, vaccines cause autism, measles is safe) will reinforce these beliefs by seeking out like-minded people who share their ill-founded and alarming viewpoint (“value homophily”).
This will make members of forums such as JABS less likely to ever accept that they are just plain wrong. Not only do they hold a faith-based position, but they further entrench themselves into this position by seeking out those who agree with them. Oliver Burkeman reports in his Guardian column that Ethan Zuckerman claims that “homophily causes ignorance” – and Zuckerman could well be right. Burkeman uses the example of another “controversy” – but instead of MMR and autism gives us “[homophily is] also why, say, creationists imagine that the debate over evolution is an active and unresolved one: in their social circles, it is” [my italics]. As McPherson, Smith-Lovin and Cook put it “[h]omophily limits people’s social worlds in a way that has powerful implications for the information they receive, the attitudes they form, and the interactions they experience.”
http://en.wikipedia.org/wiki/Homophily; Ethan Zuckerman; Oliver Burkeman; http://www.librarything.com/ (mentioned in Burkeman’s article – looks pretty cool); McPherson, Smith-Lovin and Cook in the Annual Review of Sociology.