Not a bad idea. I guess the UX is not hard, but likely it would clash with GH's bias towards openness/transparency/public record. Possibly risk making moderation 1st class citizen, they may fear this would detract from the main purpose of collaborative code production. Yet...it could help that. But I understand it's a tricky nuance.
So, they have comment minimization by assigned moderators. Or you can just delete / edit comments and issues. Obviously not as powerful as a pre-screening queue. Less work tho!
