There has been hardly any evidence that the "Momo thing" was anything at all, and that's being generous. From https://en.wikipedia.org/wiki/Momo_Challenge_hoax

There has been hardly any evidence that the "Momo thing" was anything at all, and that's being generous. From https://en.wikipedia.org/wiki/Momo_Challenge_hoax https://en.wikipedia.org/wiki/Momo_Challenge_hoax: "web security experts and folklorists studying urban legends have stated that the phenomenon is likely a case of moral panic: a sensationalized hoax fuelled by unverified media reports" Maybe the image was inserted into undesirable videos, but the image itself is harmless and inoffensive. It's simply a (model of a) girl with enlarged eyes. Automatically banning specific legal and inoffensive images is a huge overreach by Facebook, because what other images could they be banning?