While it can easily be argued that deviantART is simply a cross-section of society, with the good, bad and ugly all mixed in, I think there's something else that needs to be looked at. deviantART (known as "DA" to members) allows many different kinds of art, including many things that to the average person would qualify as disturbing evidence of emotional and psychological problems. As a Policy Violation Administrator for 3 years, I saw literally everything you can think of, including underage nudity, grotesque corpse photos gleaned from the web and submitted as 'original work,' thousands of photos of sliced-open arms and other body parts and more. While DA does have certain guidelines for the submission of work, these rules can be ambiguous at times, and interpreted differently by different administrators.
DA boasts an environment where all are welcome to submit their work, be it a professional photographer like Chris Weeks, a renowned painter like Aaron Jasinski, or simply a eighth-grader who wants a place to show pencil or color drawings. Even though the premise is interesting - even revolutionary at the beginning - the trend at DA over the last few years has seen a serious rise in "crap art," or low-grade work done by untrained amateurs with debatable talent.
The frightening thing about such an environment is not the number of poor artists, however. It's the number of emotionally or psychologically disturbed members of the community who are able to find each other through the common interface of forums, comments, and submissions. Administrators can ban troublesome users and remove offensive pieces from public view, but with a community of tens of thousands of people it is nearly impossible to catch everything. Sadly, much of what is caught is whitewashed or simply ignored.
There are always signs. Sarah Kolb, murderer of her classmate, was involved for some months in a harrassment situation, leaving constant insults and even death threats on the userpages of other members. While her and the other parties involved were all banned repeatedly, the comments themselves remain, a terrifying insight to the mind of a killer. Another minor posted a series of photos depicting his minute-by-minute torture of a gecko lizard. The photos spanned a three-day period until the lizard finally died, much to the frustration of his captor. Ben Fawley's userpage shows a 3D rendering of a human skull, with cryptic references throughout his commentary and journal.