The fact that you think this is going to get decided by a judge is at the root of your misunderstanding.
Nobody can afford to be defending the thousands of cases that would be brought against platforms over user-generated content if there wasn't a simple knock-out rule to get them dismissed. It doesn't matter if you're doing something reasonable, somebody would argue that you're not because there's still enough chance they might win and get awarded millions of dollars. And even if you win you still had to spend a million dollars on lawyers to prove it to a judge, and then someone else files a new lawsuit next week.
So the platforms can't just be right, they have to be so far away from the line of wrongness that they can get claims against them dismissed out of hand. But since it's inherently a trade off between false positives and false negatives, getting right up next to the line without crossing it is what you really want (that's the middle ground), and then that's off the table. Which leaves avoiding liability by not moderating at all or avoiding liability by moderating hyper-aggressively beyond all reason, since those are the two options to keep it from needing to be decided by a judge (which is the thing that bankrupts you).