The content and vision of the founder for that content is what draws people to Wikipedia and stack overflow.
That it takes people who occasionally need to be assholes in order to maintain that vision and ideal is a failing of communication to the out of sync contributors... and those contributors to follow that ideal.
There is nothing stopping anyone from forking the content stack overflow or Wikipedia and providing a different vision. If more people follow that new vision, it wins and the world shifts to a different site (that is what happened with experts exchange).
The main problem with the fork however, is getting the people who contribute good material and don't want to have to read jokes about exposed buttocks on the moon or favorite comic strip amidst documentation for Java.