|You know it makes sense|
"The Savage Curtain" (TOS): War, peace, good, and evil
This is the one where the Enterprise encounters Abraham Lincoln. Kirk and Spock beam down and meet up with Surak. It turns out that some rather interesting rock-aliens want to understand the humans' concepts of "good" and "evil" and have arranged a fight between four good characters and four historic villains. Kirk and Spock at first decline to fight, so the alien arranges that the Enterprise will be destroyed unless they beat the others.
One of the common objections to the episode is a simple chronological error. One of the villains is Kahless, the founder of Klingon warrior culture. In most of Star Trek he is a revered figure, so why is he a villain? Of course, these are not the real people but projections from the humans' expectations, so you can say that this is Kirk's anti-Klingon prejudice. But the real answer is that the positive view of honourable Klingons starts with TNG. The TOS Klingons are militaristic villains. We don't really know much about them, and we do occasionally glimpse things from their point of view, in which the Federation is the villain. But this is the first time Kahless appears. It's TNG and its successors that altered his significance. If you insist on a consistent "canon" then the "Kirk's-prejudice" explanation will do, but it is not reasonable to criticize the writers because their version isn't consistent with a later revision.
Another criticism is that Kirk is strangely credulous about Lincoln, when he ought to know this must be some sort of trick. But this is raised in the episode, with McCoy and others warning him. In particular McCoy notes that it seems quite a coincidence they created a replica of one of Kirk's personal heroes, and Kirk is the one who will be deciding whether to beam down. Kirk tells them that he knows it an illusion, but a Captain's Log entry seems to suggest that he finds it hard to resist the illusion.
It has got its faults, certainly. However, there are some very interesting aspects to the episode.
Possibly the most important is Surak. This is the first time we encounter him, and we learn a lot more about the origins of Vulcan thought. Spock does not believe it is Surak, of course. But, as with Kirk, he can't help behaving as if he did. When Surak refers to the emotion he saw in Spock's face, Spock apologizes. Barry Atwater's performance as Surak is striking. He has presence, he conveys intellectual and moral strength—and a touch of arrogance, the necessary self-confidence of the reforming leader who knows he has the answers. He tells Kirk of the devastating wars of the Vulcan past, and of how some went to the other side to talk peace. "The first were killed, but others followed."
Surak goes, to talk peace, and is killed. Lincoln, trying to rescue him, is also killed.
Kirk and Spock eventually prevail. The alien is a bit disappointed. Evil runs away, it notes, but in general good and evil seem to use the same methods and aim at the same results. Kirk ripostes that the others were fighting for power (which they had been promised) while he and Spock were fighting for their shipmates' lives. The alien says "I perceive", but it sounds like "Yeah, whatever."
At the end there is an interesting exchange between Kirk and Spock. Kirk comments how real they seemed, especially Lincoln (who had, we learnt earlier, always been one of his heroes). Spock points out that since the illusions were drawn from their own thoughts, they were inevitably just what they expected. This is worth thinking about. We construct our mental images of heroes, both present-day and historical, according to what we know but also according to what appeals to us.