This is not new. Many of the mailing lists that dominated the discourse of the early Internet in the 1990s operated under a similar rule. The novelty is that it disappeared almost entirely for decades.

The original purpose (on the Internet) was to create a space where complex ethical and moral questions could be explored and discussed in depth without risk of someone taking a hypothetical statement out of context to slander you, as people are wont to do. It would be orders of magnitude worse in this current age of people obsessed with generating click-bait for engagement, which wasn’t a thing back then. I personally found that environment to be intellectually stimulating and rigorous, I miss the standard of discourse of those days.

Chatham House Rule is going back to the old Internet, which valued novel insight and reasoned discourse highly, before the masses took over the Internet. The purpose was not to enable edgelords. Rational defense of ideas, statements, and hypotheses was expected and table stakes. Related rules of that era, such as Crocker’s Rule[0], placed responsibility on the reader to address uncomfortable or offensive feedback in the most dispassionate way possible.

[0] https://news.ycombinator.com/item?id=12881288