I wonder if the postmodern turn wasn't to blame. The critique that it fostered was a good idea in many ways, questioning our claim to be 'unbiased' and fostering a wave of supporting populations who often have few resources and little power. There is no reason why moralism and advocay can't be a part of anthropology.
However, there were also strongly negative effects. People took the disciplinary soul-searching to an extreme, hence moralism and advocacy coming to dominate as people attempted to correct for the past. There seem to be fewer recent ethnographies insisting on 'reflexivity', but the discipline still has a very strong political bias. In other words, we critique the mistake of believing we are 'objective', but we fail to step back and critique our present subjective analyses. A good example of this is the current fashion to critique neoliberalism. I have no problem with people using the term, but few people who use it seem to feel obliged to explain how and why they are using it. Neoliberalism seems to be the new globalization.
The effect of this kind of non-critical approach is that it makes the writing look like an opinion-piece and downgrades its status as evidence. Tere is no way of stopping this trend as far as I can see, apart from by non-critical rejecting books and journals that we review, and by trying to teach students to truly consider all evidence rather than following fads. However, fads tend to change fast, so it may be mostly a question of riding it out.
Reading through some of the comments here, I agree that a central shift has been the postmodern turn as Erin B. Taylor suggests acknowledgement that objectivity is no longer a feasible goal. This was tied to the reflexive movement in anthropology, I think. But I am also beginning to wonder if the shift to advocacy is not also related to how we write.
Sharon Traweek and others who study cultures of technologies and science have often reminded anthropologists of the importance of inserting themselves into the narrative and this means writing in our bias, where our funding comes from, moral agendas and taking on the role of advocate/translator/or go-between to various degrees. These aspects have always been present in all anthropological research from Boas onwards but they never made their way into print and are therefore largely invisible giving the illusion of not having existed.
Not only are we putting more of ourselves into texts - texts which are no longer only journal articles or books, but blogs, tweets, magazine articles etc - but these texts are more widely read and circultated which ultimately means that our research takes on new significance and becomes more than just discovery or explanation. I think that the work of Gabriella Coleman on Anonymous is a great example. Coleman has academic publications which are quite traditional in tone and yet with twitter, interviews by Huffington Post etc her work borders on advocacy and can be understood as having a moralism - even though Coleman herself might not explicitly intend it to. It is almost as if we are Malinowskis, writing out academic papers but simultaneously publishing our diaries for all to read, giving our 'official' work a completely different context for interpretation.
Just some Sunday musings... Thanks Philip & everyone on the thread for an interesting discussion.