Recently, I've noticed an interesting failure mode in some communities I've observed online.
In this scenario, there would be some kind of content that appealed to certain users, but that many others wanted to avoid seeing and indeed considered undesirable (gossip/drama, angry political arguments, sexually explicit content, etc.). In order to prevent this content from "bleeding into" conversation, administrators would create new channels where this sort of thing could be quarantined away from normal discussion (or repurpose existing channels to sequester this content), thus allowing people who wanted to avoid this sort of content to avoid having to deal with it.
However, at least from my perspective this sometimes had a bit of an ironic effect. Once the "containment area" was established, there was now an obvious affordance for this type of content that did not exist previously. As a result, the quarantined content would actually become much more prevalent in the community - further, in some cases newcomers would join the community looking for one thing, see the quarantine channel, and think something along the lines of "wow, I never knew this was a community for <insert undesirable content here>!"
The net effect of this was that the quarantines often backfired; meant to isolate undesirable or controversial content, they instead made that content more prevalent in the community as a whole, even if people no longer had to encounter it in general channels.
The chief lesson I draw from this is that it can be better to simply forbid unwanted content rather than creating a quarantine for it. If there are truly people coming to your community in large part for something that many would rather not have, you may not want them there; further, there may be those who are driven away by the presence of such content, and insofar as the undesirable content presence increases the latter group may become significantly larger.