The last bastion of "civilization" is in fact a bastion of tyranny about to fall to the noble "Yankee" resistance.
...Meaning the noble resistance has become the tyranny, and worse.
You may believe that, and it would be the saner interpretation of such events: but again, it is quite clearly not the stance
the episode takes.
But the idea that the Kohms would have been evil first is bullshit.
The cues for how the audience is meant to react to these events come from the protagonists. When Spock and Kirk tell us that the Yankees have been fighting to regain land stolen from them by Asiatic conquerors, they are very clearly
not being presented as talking out of their asses -- and given that they are talking about
communists and
Asiatics, which are two stock names of evil for Sixties American audiences (who are in the midst of the Cold War with Russia and China and who vividly remember Japanese perfidy in WWII when this episode airs) this is not a surprise. Their speculation is being treated seriously by the story and is borne out quickly by words and behaviour of Cloud William.
Owing to that, your speculative reading is not a plausible in-context reading of the script. I'm sorry, it just isn't. But you're right to be disturbed by the idea of the script having such a premise, because it
is disturbing. It means the Yangs are being presented as a relatively noble cause
even having exterminated most of the Kohms, which effectively means the script and our heroes are tacitly telling us such measures may be acceptable as a way of overcoming communism if it comes to open war. Sure, it's a little overzealous -- the Yang cause is still presented as
savage -- but it is not presented as evil by any stretch.
The Kohms, now finding themselves on the losing end of the war, are pretty clearly using Tracey for his weapons technology.
And that's unfair to you, because they are Commies? Makes no sense.
It's not a question of its being unfair
to me. Once the Kohms have been framed as Asiatic Communist land-stealing bad guys who are being given their comeuppance by a resistance of noble Yankee savages, the contextual cues as to how to read their behaviour are being made inescapably, utterly clear.
But there is no reversal. We learn nothing new about the conflict at any point.
No, you're trying to ignore the interpretation the protagonists present and the way the events are shown to bear out that interpretation, and you can't do that. That's cherry-picking.
At no point does it mention the American Constitution playing a role in the conflict.
It's the holy book of the Yangs. Of course it's mentioned.
They can't read the Constitution, and thus cannot act on its contents, least of all adopt them as their life guide.
The Yangs are descended from its writers and, garbled though their now-degraded oral tradition about its contents has become, the basic character of their society is still owed to it: they
noble savages in the classic style, austere and honorable in their own way to any enemy who isn't a Kohm. Kirk is required to instruct them and
complete their freedom, he is not presented as its source.
Now that's a completely different issue.
No, it is the same issue. The heroes
are our window on the story. They
are our source of facts. The story is specifically crafted to suggest that their interpretation of events is correct. There is no lack of clarity as to what the writers believe and want us to believe is the correct and factual interpretation of events on Omega IV. None.
That you don't like this interpretation is understandable. It's unpleasant and hypocritical and jingoistic and racist and effectively winks at genocide without owning up to doing so. But it is
not in the least bit unclear that this is the interpretation audiences were meant to come away with. That they're not the boss of you is fine, good for you, but that doesn't change the very clear cues given throughout the story. You don't choose to see the Yangs as the good guys; it is very clear nevertheless that the script is presenting them as the local good guys, or at minimum the lesser local evil. There is no way around that.