Whenever there is a demonstration or event, there are people who are there for a multitude of reasons. And usually not all are the ones the organizers or primary event goers have in mind. The demonstrations in Ferguson are an example. All was swimming until less than a dozen thugs woke up and decided to loot another store. Those same thugs threw bottles and mouthed the usual revolutionary and violent nonsense. And some of them wore masks. The community of demonstrators tried to stop them, but as always with hard heads they weren't interested in being stopped. That is where police are supposed to make arrests.
The incident reminded me of my own experiences. I was a member of WSFA, and am still mentally one. It's still around. Like the Ferguson demonstration we had meetings, we had people attending for all kinds of reasons. And we hosted an annual "DISCLAVE" convention in a hotel each year. Alternating with a "Balticon" because our memberships overlapped with the brother Baltimore based Science Fiction association. We were united by a love of Science fiction. But our members loved comics, Goth, Orthodox Jewry, Ayn Randian athieism, Orthodox Catholicism, Unitarianism, every other Protestant Church, Mormons, mainstream Atheism, New Age religions, Paganism, and just about a cross section of the educated of the two metropolitan areas. It was a lot of fun planning for the conventions and seeking to attract authors, vendors, and others. We rarely got the famous Hollywood types, but we had as much fun planning the conventions as having them. And our Baltimore club was the same, only better. They (we also) had a clubhouse in the Eastern Part of the City that used to be a theater.
One year we planned our DISCLAVE over at the Ramada Inn in Hyattsville. And it was a disaster. The event itself was fun. Was entirely peaceful, and enjoyed by everyone. But during one of the nights a couple enjoying kinky sex in their private room thought they could handcuff themselves to a sprinkler. The Sprinkler broke. The system went off all on that floor. And enough water came down to flood that floor and all the floors below it. I'm sleeping with my kids (who were just becoming teenagers) in my room when the alarms go off and we all had to go to our cars. The Power was off, and the place was ruined. This proved a blessing for the Hotel as they were due for rennovations anyway and our and their insurance paid for them. But we were banned from holding Sci-Fi conventions and ultimately had to rename DISCLAVE to something else. No more DISCLAVE. They call it CAPCLAVE instead. Works for me. I'm still an original nerdist.
What had happened was a group into kinky and Sado-Masochistic sex was parasitising our conventions. Most of them didn't have overlapping interests, they were there to party and do something they couldn't get a Hotel as a group on their own to do. We had to change our bylaws to be more restrictive about such things. This occured in the late 90's, just before I started dating my wife. She wasn't too much into Sci Fi, and her interests were more hi brow so I couldn't attend WSFA after that and don't know how they came back, but I know they did fine. The point is I've seen this sort of thing with political groups, demonstrations, and it also occurs within organizations as folks take advantage of people to do their personal business on the sly. It happens, and blaming folks for the people who take advantage of them is unfair -- unless they let them continue to get away with it.