I only partly agree. 3D printing undercuts the market for low-volume cheap plastic items. Similarly, self-replicating robots could undercut the market for low-volume robot arm designs.

For factories in conventional situations, I agree that non-self-replicating equipment would be cheaper than self-replicating equipment for manufacturing the same goods.

Self-replicating robots are clearly cheaper than non-self-replicating ones in a few situations:

• If there is a high cost to scaling up or down a factory, and demand often changes suddenly.
• If it's expensive or impossible to ship new equipment from a large scale manufacturing plant to the location it's needed (e.g. Mars).
• If there are natural resources to support an exponential growth scenario (e.g. a fully automated factory that can take in raw materials from a resource-rich planet to build more factory parts).
• If the production equipment (including repair equipment) is often damaged and requires constant repair (e.g if individual self-replicating units are routinely destroyed by viruses or cosmic rays).