There is nothing wrong with the Reddit approach of having different communities with different moderation policies (well, except for the many edge cases you point out.) But presumably the unspoken motivation behind TFA is moderation on Twitter which is a very unique site that does not have specific “walled garden communities” with their own moderation, and is uniquely porous. If you want to use a moderated (ad-supported) site that lets each user define their own community, then you either need some global base moderation policies or else you need aggressive client-side filtering (and advertisers had better trust that it works effortlessly, since it will be their ads showing up next to the genocide posts.)