He's written about it several times, here's the main article: https://www.techdirt.com/2019/11/20/masnicks-impossibility-theorem-content-moderation-scale-is-impossible-to-do-well/
The main idea, at least the way I look at it, is that at small scale, it's possible to have an actual shared context and shared values. This is impossible at large scales.
@burly @mastodonmigration
Here's a specific example where moderation without context makes a (relatively harmless in this case, and funny) decision: https://www.techdirt.com/2022/09/23/the-most-famous-blunder-of-content-moderation-do-not-quote-the-princess-bride/
The Most Famous Blunder Of Content Moderation: Do NOT Quote The Princess Bride