"This sounds chaotic, but most of the time the "unhelpful" or "inappropriate" changes are quickly fixed by human stompers and algorithmicised helper bots. Without the kooks and the insulters and the spray-can taggers, Wikipedia would just be the most useful encyclopedia ever made. Instead, it is a fast-paced game of paintball.
"When, last year, some computer scientists at the University of Minnesota studied millions of Wikipedia edits, they found that most of the good ones - those whose words persisted intact through many later viewings - were made by a tiny percentage of contributors. Enormous numbers of users have added the occasional enriching morsel to Wikipedia, but relatively few know how to frame their contribution in a form that lasts."