I can't really see a relevance between "we should spend more time with trusted people", which is an argument for restricting who can write to our online spaces, and "we should be unindexable and untrainable", which is an argument for restricting who can read our online spaces.

I still hold that moving to proprietary, informational-black-hole platforms like Discord is a bad thing. Sure, use platforms that don't allow guest writing access to keep out spam; but this doesn't mean you should restrict read access. One big example: Lobsters. Or better-curated search engines and indexes.