Reddit's /r/place is perhaps an interesting counter example. It started that way, but as space on the image grew tight and contested, all of that kind of stuff went away. Towards the middle and end, the only significant images were those which could get enough people on board to maintain, and people tend to care more about other stuff, it seems.

I'd say it comes down to the balance of (# of people who make a positive impact * difficulty of positive impact) vs the same for negative impact.

Wikipedia is another example. Sure plenty of people make stupid edits, but enough effort is put into detecting and immediately reverting the vandalism that the effort required to properly vandalize it quickly goes beyond the effort most people will go for a stupid joke.