Star Trek: The Original Series: The Joy Machine

Timshel was once the vacation spot of the galaxy, full of culture, natural beauty, and friendly, hospitable inhabitants. But now Timshel has cut itself off from the universe. No one is allowed to enter or leave. Concerned, the Federation has sent agents to investigate, but none have returned.
Captain Kirk and the crew of the Starship EnterpriseTM are shocked to discover the truth: the people of Timshel have succumbed to an insidious new technology that guarantees every citizen total pleasure, a soul-destroying ecstasy that has enslaved their entire civilization. Kirk and Spock have faced many threats before, but now they face the most seductive menace of all: perfect happiness.
And the rest of the Federation may soon fall under the irresistible control of the Joy Machine.