Well, legislation + policing + prosecution + courts of law with due process are precisely that - manual moderation of social behaviour at massive scale (admittedly not billions, but hundreds of millions of individuals). Yes, endlessly complicated, yes, costs a fortune, yes, riddled with flaws, yes, it becomes a political problem, yes can be very emotionally challenging (I know because my wife is a criminal public defender. A bad day for me is when a sprint is late. A bad day for her is literal rape, torture, murder, injustice. Definitely puts things in perspective. But she knew what to expect, has a balanced workload, is well compensated and believes it is for a greater good. If facebook is structuring things in a way that people are being crushed - I've read those articles too and don't doubt it - shame on them). But 'it's hard work' isn't a very good excuse.
To be clear - I understand your point and sort of agree with it from a software engineering perspective; I just don't think that's necessarily the right perspective here. Every day we demand that governments and companies in all sorts of different industries do lots of hard, complicated, not-easily-computer-programmable, bug-riddled human processes requiring subjective judgement because they need to be done.
People & organisations aren't entitled to only do the things that need to be done which they can do with near-zero marginal cost with computer software - when they can do that, good for them. When they can't, tough.
Yes, I agree, from personal experience designing good Recommendation Systems is hard. That's a field I'm interested in too - out of curiosity what alt-tech sites have you tried? Would be interested in also trying them and exchanging notes.