While this certainly makes it much less likely that costly massive human moderation would actually be implemented, I don't think that really qualifies as an arg

While this certainly makes it much less likely that costly massive human moderation would actually be implemented, I don't think that really qualifies as an argument for why it shouldn't be done. If you think rossdavidh is right about those issues Facebook is having (and I think he's right), then that's the reality in which the company has to operate. If a business model leads to infeasible costs due to fundamental issues, maybe that business model shouldn't exist as such. Obviously Facebook (or any other company) doesn't want to do anything that significantly increases their costs without providing revenue if they can avoid it, but that doesn't mean it shouldn't be expected of them.