The obligation on content platforms is not to allow any legally permissible message to be posted. It is to prevent any legally impermissible message from being posted.

Moreover, as a business, just because something’s theoretically legal, if it exposes you to a nonzero risk of being prosecuted - even if you are pretty sure you will prevail - you’re well within your rights to elect not to be the vehicle through which that bit of caselaw gets made.

The claim that 90% or so of these deleted messages were ‘legally permitted’ seems to rest on a somewhat untestable hypothesis that if these platforms had left this content up, it would not have resulted in legal consequences, or if it had, the hosting platforms and posters would have been exonerated.

Whether or not to make those gambles with facebook’s shareholders’ money is really facebook’s business.