Gideon finally consented to the Bureau's request in 2268. The physio-cultural reports submitted by Gideon to the Federation described environmental, physical, and cultural conditions that indicated that the planet was a literal paradise. This was, in part, due to the planet's germ-free atmosphere, which – combined with their love of life – lead to the inhabitants' ability to regenerate their bodies and increase their life spans.
With the absence of disease, the birthrate far exceeded the planet's death rate. Death only occurred when an individual's body could no longer regenerate itself. By the mid-23rd century, the population explosion on Gideon inevitably saturated the planet to a point of being a living mass of individuals. To keep this fact secret, the planet had screens placed around it so as to prevent ships from scanning the surface. They also made the specific request that no scan attempts were to be made by orbiting vessels.
When the USS Enterprise finally arrived on stardate 5423.4 to conduct negotiations, the Gideon Council wished only to allow a single Federation representative to visit the planet: James T. Kirk. The Gideon Council, aware that Kirk was a carrier for Vegan choriomeningitis, chose him in a radical attempt to solve their overpopulation problem.
Ultimately, Kirk was used as a means to introduce the disease, on a voluntary basis, to the planet's population. This was done in an attempt to introduce death back into their society and to end their malaise caused by overpopulation. (TOS: "The Mark of Gideon")