A few years ago, while doing a project where they had to research a historical figure that related to a member of their family, a student of mine came across this website and promptly decided to change her historical figure. Her reason was not for any of these blatantly racist statements but that buried somewhere in that sludge was a claim (supposedly backed by evidence) that King had plagiarized his doctoral thesis (and that he had beat his wife.) Since much of the class (an intro for first year college students) had focused on plagiarism as a scholarly error to be avoided, and on the importance of tolerance and the consideration of various perspectives, this reason made some sense. If you read the essays on the site, they seem well researched and, like all subcultural regimes of truth, seem to adhere to the methods of credible research.
I had to do far more rhetorical backflips than I thought were necessary to say that, even if some claims on a blatently racist website could be proven, this did not make it a credible source. In saying this, I inevitably had to give more credibility to this source than I normally would have. And, most importantly, I was in a position where I could hardly rely on some hagiographic account of King to repair the student's impression--mostly because I don't think hagiography is good scholarship. In the end what I took away from this was that I hadn't sufficiently instilled in my students the sense of how to examine a source for credibility, but at the same time I knew that many of the methods for considering this were present on the site in question.
This interaction was also limited by method, but I also think that, outside of telling her that MLK was a good man no matter what anyone said, only a more rigorous method could have helped. My sense is that this is what Horkheimer and Adorno (w/ Lowenthal) mean by the dialectic of enlightenment. I know there is a larger argument about scientism going on here, which I have only been able to partially absorb, but they seem to see the concept of Enlightenment as being both its own problem and its own solution. Which seems to suggest the need for another value system outside to guide it. But it doesn't seem to indicate that we are better off doing away with it altogether.