#scifi idea...
Someone makes a "replicator" [star trek not star gate] and one key thing it can make is another of itself.
Set up to make food, drink, clothes, medications, soap and stuff. With some security (prescription drugs if you show a prescription, alcohol if you show an ID, all good).
How quickly would it spread (replicates itself).
How quickly would all fast food, supermarkets, restaurants, all see sales go to zero, and go bankrupt.
Would any governments dare to try (LOL) to ban it?