If you are only using Facebook for its original purpose of keeping up with old friends and family, then it doesn't actually have the scaling problem: if one of your friends or someone in your family starts posting a ton of racist bullshit you either confront them about it or drop them as a friend (preferably bilaterally), and either result is actually better for society than having Facebook attempt to present a skewed view of them that tries to just pretend they aren't posting all of the horrible stuff in the first place (whether by blocking it from being posted, quickly removing it once posted, or running some complex ranking algorithm that does a good job of hiding it).
It is only when you start having strangers talking to strangers that you run into a need for moderation, and even there you should be able to scale by sharding and punting the problem to others: if you have a group--similar to a real-world club--the moderation is on you, as the issues in your community shouldn't leak to people who haven't joined your community (and if people leave your community because you fail, all the better). The only real issue is that Facebook wants to--for the increased engagement, and thereby ad revenue--run a ton of recommendation algorithms that shove content from people you have no affiliation to in your face constantly (which one might notice should already be considered antithetical to the design of a social network) which leads to a ton of stranger-to-stranger interactions that are entirely "on Facebook" to ensure are clean.