Story, first published: The Magazine of Fantasy and Science Fiction, Jan. 1961
An alien offers humanity a vaccine that will cure all ills for life - free of charge with no strings attached. He makes the offer to a poor small town doctor in Millville. The alien has difficulty in understanding the economics of the human medical profession. Doc Kelly defends the system: "We are doing all we can to destroy our jobs." But the alien counters, "This is fine ... It is what I thought, but it did not square with your planet's business sense". ...
On the eve of "Operation Kelly", when world-wide clinics will administer the vaccine to all humankind, Doc has second thoughts. Millville had been the pilot project, and the doctor discovers that he, like others in the town, is losing some of his mental sharpness. He cannot but wonder: has intelligence also been a "disease"? Would the aliens so limit humanity's powers of self-destruction even if it meant reducing him to abject stupidity? He is willing to take the chance: "Doc had been a doctor too long to stop Operation Kelly".
Ewald, Robert J.: When the Fires Burn High and the Wind is from the North, p.54-55