Now hold on just a second, there.
This wasn’t one of those episodes where history just happened to unfold so as to look a heck of a lot like Earth back when – be it that planet where people independently developed the American flag and recited both the Pledge of Allegiance and the Preamble to the Constitution while opposing Chinese-looking Commies, or the one with a Roman Empire where guys with names like “Maximus” and “Claudius” watch gladiators fight in the arena while those who follow the Son of God preach nonviolence, or whatever.
It wasn’t even one of those episodes where Federation meddling had increasingly swept the planet to produce an entire worldwide culture based on '20s-era gangland Chicago or '40s-era Nazi Germany or whatever backlot was available at the time.
It was that our heroes met a bunch of I Said No Trespassing telepaths, and realized from the start that everything they saw was a fake-looking illusory construct being dreamed up at them – complete with a saloon and gunslingers and whatever other bits-and-pieces details Jim Kirk figured were pulled out of his mind, for reasons that got patiently explained to him. It’s not some alien planet where the OK Corral was around before they arrived; Wyatt Earp and Doc Holliday and all the rest weren’t actually down there until the hallucinated scenario started to play out – sure as our heroes eventually bull their way through that contrived situation by concluding that imagined bullets can’t really kill them.
The aliens, now suitably impressed, dissolve the illusion and start talking diplomacy. And they’re a bit perplexed:
“Captain Kirk. You did not kill. Is this the way of your kind?”
“It is. We fight only when there’s no choice.”
They’d apparently expected something more primitive – and with good reason:
“You wanted to kill, didn’t you?”
“But he didn’t kill, Mister Spock.”
“But he wanted to, Doctor.”
“Is that the way it seemed to you, Mister Spock?”
“Yes, Captain.”
“Mister Spock, you’re absolutely right. That’s exactly the way it was.”
Whereupon they end the episode with one of those classic Roddenberry back-and-forth-and-forth-and-back discussions about how mankind sure was a heck of a lot more ready to kill back then, such that humanity’s survival depended on overcoming our instinct for violence, such that a vast alliance could someday get built around like-minded people who share a belief in establishing peaceful relations while seeking out new life and new civilizations.
Plus you’ve got Uhura referencing her knowledge of Swahili, and McCoy trying to kit-bash the right compounds for improvised tranquilizers, and Spock doing the Vulcan mind-meld and Scotty knocking back a stiff drink, and nobody saying Brain And Brain What Is Brain – so what’s not to like?