Your implication here seems to be there should be different rule sets, one for small forums and another for giant social media. So, I don't have to monitor every post but Facebook has to, right?

But that doesn't mesh very well with your original post, does it? You argued that if it's impossible for Facebook, Twitter and other social media to monitor every post, then they shouldn't exist.

I'm sorry but it's not OK to create a rule just for Facebook that's impossible for Facebook to follow. If you want to outlaw Facebook, there are better ways than this Kafkaesque circus.