>moderation quality goes down enough that being on the site is no longer fun.

I'd say that Reddit (and really the internet as a whole) hit that years ago. Another user said this on a different thread, but Reddit has this deep depression inside it that isn't really noticeable until you leave. Like, you don't ever really see happy people on there anymore, just people with varying levels of misery. I don't think that's really unwanted by Spez and Co, either. If there's something that the internet has taught me, it's that it's easier to retain audiences by keeping them miserable and afraid than it is by keeping them happy.