. . . but would he have done so [messed with the Body] without a threat to the enterprise?
The Apple also had a threat to the E. Does he mess with a happy-but-stagnant culture when there's not a threat? Paradise Syndrome has a threat, right? Darn, it would make a better dilemma and argument set-up between Spock and McCoy if it were a "pure situation" with no contrived threat. Then the threat/suspense would be to Kirk's character, depending on how the viewer sees it. Intervening would make him an imperialist to anti-imperialists; leaving them alone would make him morally weak to those who believe in the need for strife, struggle, and growth.
Somebody write that ep. or novel, wouldja? I'll buy it.
And remember, NO THREAT to the Ent. or plague on Whoziz IV that needs that serum to rendezvous with the USS Ludington in time!
Setup/exposition; proposed way to mess with culture and introduce strife; arguing about prime directive; decision and implementation; denoument; scene of Ent. flying away with Kirk promising a team of advisors.
There, I've done the hard part. Someone take a handfull of uppers like it's Sixties Hollywood and flesh that out overnight.