If you ask 10 good, experienced, human moderators whether a controversial post is allowed, you'll probably get at least 15 different answers and justifications.
FB would probably find it harder to train from this, as each moderator will be using different justifications, and reaching different decisions.
At FB's scale, they want something cheap and straightforward which they can implement automatically and go Kafka on the lack of appeals. The reality people need to wake up to is that when a business is at FB scale, people who fall through the cracks due to a broken algorithm simply don't matter. Google doesn't care if you get locked out of your Gmail, in the same way FB doesn't care if you get spuriously banned.
When users place more value on a service than the service places on them as a customer, it feels like a market failure scenario that leads to these kinds of outcomes. When the go-to price is $0 though, it isn't clear how you resolve this.
But 2 (scale) makes this solution to 3 and 4 expensive / impractical.
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.