As noted in my above response to moondog, it is not as simple as saying the desire for celebrity motivates all mass shootings, because many factors can be critical, and overlapping motives are not uncommon. When mental illness leads to mass shootings, of course, no rational motive is required. As particularly noted in my response to moondog though, the line between seeking vengeance on society or merely fame is usually blurry. Taking vengeance on a group without it knowing who is responsible or even that anything happened is rather difficult, so fame is usually a required means even when not a true goal. That may or may not cover basic alienation, depending on whether the latter leads to active hatred of society or "only" replaces empathy with apathy.

Mass shootings are, regrettably, frequent enough to have varied primary causes. Fame can be among them, as is suspected in the Aurora shootings: http://www.abcactionnews.com/dpp/news/psychologists-suggest-accused-killer-james-holmes-was-seeking-fame So can vengeance, as in the Ft. Hood shootings. So can mental illness, as in the UT Tower shootings. Dissociative alienation did not prompt witnesses of Kitty Genoveses murder to kill anyone, but it seems likely it did allow many of them to sit idly watching her brutally raped and murdered without even bothering to call police. There are no one-size-fits-all solutions, but every reasonable preventive step would be welcome at this point.