Headscratchers: The Day the Earth Stood Still (1951)
Why did Klaatu have only one science advancing item, if only so that more people could look at them at once?
And why did he think that advancing on an obviously violent race without saying a word and while holding an item that popped open unexpectedly once within melee range was good diplomacy?
Clearly Klaatu's people need to rethink their First Contact protocols.
Why are the world's nations being such hard-asses about meeting together? Why does Klaatu have to speak to them all at once, in person, in one room? Can't they just invite the TV news from every country?
Put this in the context of 1951. This was only 6 years after the end of WWII. The anti-red hysteria was rolling towards full steam. There was a shooting war going on in Korea. Both the US and the USSR were deathly afraid of the other launching a nuclear attack. TV was in its infant stages. And maybe, just maybe, Klaatu thought it important to speak to all of the world leaders face to face.
If they can't agree to meet in the same room to hear a message from a highly advanced alien being, why should anyone believe that they are capable of learning to behave peacefully? It's a Secret Test of Character.
The Aesop! On the surface it's "end all war and embrace world peace!" but since Klaatu gets this message across by threatening Earth with Gort, it comes more across as "embrace peace or we'll render you extinct!" You can't force a species to accept peace through threat of annihilation, that's been done time and again in tv, movies and books, but it's often a villain's goal.
Minor quibble: he said the aliens don't care if we never give up our warlike ways and blow ourselves up, it's if we try to blow any other species up that we face death by non-mutant-laser-cyclops-bot.
So more of a 'Keep off my land' sort of thing. Than a 'you kids play nice now.'
A little bit of Fridge Horror. Klaatu's benevolent and peaceful organization of planets has put the instruments of law and order in the hands of a robotic police force. They're just machines, and so they are not susceptible to corruption, coercion, bigotry, or bribery. But neither can they interpret, or even understand, the laws they've been programmed to enforce; they can only follow orders, identify violations of the law, and mete out appropriate punishment. Unless the robots like Gort are only used for big things like national defense or foreign relations, this means that the galactic justice system is nothing more than a vast machine, blind to extenuating circumstances, chugging along for its own sake regardless of the citizens it was designed to protect. The people of this organization have effectively mechanized their consciences, leaving them "free" to do anything except upset the status quo, for which they would be coldly and swifty punished. So Klaatu's warning to the people of Earth is less, "Stop being unenlightened monkeys," and more, "Don't anger the robot overlords."
"They're just machines, and so they are not susceptible to corruption, coercion, bigotry, or bribery." But what about the people who programmed them?
Could be more intended as "These are the rules you have to follow now that you have reached this level of technology. There's no skirting around the rules, for they are enforced without pity or second-chance due to the danger of breaking the rules."
But absolute, immutable rules do not account for cultural growth and change. Klaatu himself says, "We do not claim to have achieved perfection." Which means he acknowledges that his society's legal system is flawed, or at least imperfect. What is the mechanism for correcting those flaws? For changing the rules if need be? For leniency if it is warranted? If the rules are enforced solely by machines, there is no mechanism in place. A compassionate, intelligent individual like Klaatu can realize that improvements could be made, but is powerless to make those improvements.
I think it is reasonable to think systems are in place to change things if need be. Humanity has a tendency to quibble over every word and try to find a loophole in every law. They do a wrong and either try and blame someone else, avoid responsibility or play word games. Court cases can go on for years or decades because of it. Klaatu was putting it in simple terms that this is not tolerate. There are probable methods to arbitrate disputes between races, but violence is not considered an acceptable solution. If humanity tries to attack another race humanity will be destroyed. There might be a scale issue to ensure a few renegades do not ruin it for everyone, but collective punishment like this forces all humans to try and prevent a few rogue members or nations from breaking the law.