It's more likely to me that Facebook recognizes that the anti-vaxx community is one of the most active and most engaged segment of their users. Suddenly banning

It's more likely to me that Facebook recognizes that the anti-vaxx community is one of the most active and most engaged segment of their users. Suddenly banning the topic they care most about is going to trigger a mass exodus of some of their most valuable assets, while maintaining the status quo just causes a little bad publicity. I've yet to see any mass exits of users because FB isn't doing something about it, so that's the profitiable option for them.