They've sort of been caught playing with people's emotions before, although there is also an effect where Facebook look particularly bad because of how un-(self)-selective their userbase is. Everyone has a Facebook account, there are very few features to let you use it like a traditional (say) forum.
Debate on Facebook is effectively the Dunning-Kruger curve directly to your screen - not exactly that people are stupid as per se, but the level of knowledge on display is very small.
The trendsetters aren't really on Facebook anymore, too. I absolutely love memes, and there are still good, creative, meme groups on Facebook however it's literally only a matter of time before the group gets shut down because of some unexplained reason. This once again has the effect of moving anyone willing to use their brain elsewhere.
They definitely need regulating but they are also a victim of their own success.