The first 2 parts seek to reduce to absurdity the rise of wasteful wars and rule by nationalist barbarians. The 3rd part speculates that progress and exploration toward the moon and beyond is the key to ensuring a meaningful use of human talents and resources. It has speeches that some viewers dismiss as naive or bombastic but that make others tingle with excitement. It depicts a space gun/launcher and a helicopter, along with inventive mass communication devices, elevators, flat screen panels, and wireless intercoms. It's probably incorrect about windowless buildings in the future. But it portrays a child-like vision of boundless scientific/technological investigation.

To me, it seems like a movie about a group of rational minded thinkers guided by a Spinozean-like morality in their quest to immortalize themselves and live ethically through scientific advancement and a unified world government. The pro-progress characters (such as the two Cabals) believe humanity could 'live forever' by preserving our experiments and progress for future generations, always standing on our humanity as if on the shoulders of giants.

Arthur C. Clarke (author of 2001: A Space Odyssey) suggested this film to Stanley Kubrick as an example of an excellent SF movie. Kubrick hated it and said he would never watch another movie based on Clarke's suggestions (source: Clarke's special millennial introduction to his 2001 novel). Though the late Clarke kept suggesting it at the top of his list whenever someone asked him about the best SF movies. It has a beautiful Menzies art design, but mediocre special effects (esp. the toy tanks).

I personally loved it and think it excellently captures the zeitgeist of modernity. It is a bit naive about the plausibility of creating a society without crime for an extended period of time. It also seems implausible about the inevitability of progress. It seems to me we could just as easily go right back to the dark ages or at least become so stagnant in science that we kill ourselves off through overpopulation or through our inability to escape the next major natural disaster. But it nicely portrays the importance of taking risks against public and nanny outrage for potential threats of space accidents and deaths. It challenges us to choose the side of progress over petty desires for safety or comfort or happiness:

CABAL: "Too much {rest} and too soon, and we call it death. But for MAN no rest and no ending. He must go on--conquest beyond conquest. This little planet and its winds and ways, and all the laws of mind and matter that restrain him. Then the planets about him, and at last out across immensity to the stars. And when he has conquered all the deeps of space and all the mysteries of time--still he will be beginning." 

CABAL: "If we are no more than animals--we must snatch at our little scraps of happiness and live and suffer and pass, mattering no more--than all the other animals do--or have done." {He points out at the stars.} "It is that--or this? All the universe--or nothingness..." (quotes from screenplay).

If this sounds like a rationalization for devoting all of society to progress, then the council members (of the world government) will seem like technocrats. But actually those "technocrats" allow their citizens to become artisans or pursue other passions freely, and they would have to be suppressed by government bans, laws against science and experiment, and other mandates and restrictive uses of power that would turn their critics into tyrants.

In fact a huge group of rebels in the plot feel belittled by all the council's developments of science and technology, so they try to put a stop to progress and an end the council's freedom to experiment. The progress oriented council will not suppress the free speech of the rebels though, only preparing its 'peace gas' in times of emergency and merely wanting the freedom and space to pursue its progress.

So it's also a story about the freedom to do science, just as much as it's about the wonders of progress. Many people in our society would actually agree with some of these basic premises, except in cases of social bias (many want to ban cloning, for example) or naturalism (some don't want us to progress freely, and would rather we just become extinct in due time while enslaved to the earth) or fear/reason (some believe we aren't ready for advanced science/technology since we might destroy ourselves). But Cabal (the president of the council) has an answer to the problem of danger: "Our {scientific} revolution did not abolish death or danger. It simply made death and danger worth while" (screenplay).

Sentiment: positive