The nature of online content is that once it's created it can be copied quite easily, if Facebook was able to block 80% of this content that should be commended.
AI is not at the point where we can expect 100% of this content to be removed and if it was there would likely be some collateral damage that others would complain about.
At it's current state we need a lot more humans screening this type of content and who are we to subject other people to that type of mental disturbance?