I'm not blaming you, I blame Posadas, but that was a load of rubbish, and I'd like to explain why because I still find this a fascinating line of thought.

hey, on the contrary, may be on the way to exploiting all the energy existing in matter. They can use all the energy that we still do not know how to employ on Earth, and transform it into light.

There are sections like this where Posadas says what might be possible. Sure, no problem there. But then they just sort of continue on as if it is for sure possible. Maybe this is just a style of writing that I personally don't find agreeable, but I think it is not the correct strategy if your goal is to come to the conclusion that extra terrestrials probably/necessarily are using a given economic/political model.

We can conceive of a being which, just by raising its hand, can produce light, draw energy to it, push it away, and organise it. It is possible.

Then there are parts like this. Just because something is conceivable doesn't mean it is possible. I can conceive of a perpetual motion machine, but the laws of physics prevent it.

Science, on the contrary, is subject to those who finance it. Astronomers, physicists, where should they go to find the equipment for their research? They cannot do so, without money. They are not, as individuals, rich enough to pay for these things and also get by. It is the capitalist state, or indeed the Soviet state, that has the means to pay. They can thus install their equipment, but they limit their capacities to capitalist interests or the bureaucratic limitations imposed by the leadership of the workers’ state.

This is to me, easily one of the critical misses of this piece. They acknowledge that there is problems with how we support the sciences, but this problem is just handwaved, moving onto the next thing. There are more economic systems out there than just capitalism and USSR style socialism. We've made technological progress under both, and many of the others. We even made technological progress under feudalism and barter systems.

And because scientific progress can be achieved through any of these economic systems*, we can't just assume that extra terrestrials found themselves on our doorstep due to one particular economic model.

* At different rates obviously, but progress nonetheless.

All the news of UFOs (unidentified flying objects) around the various parts of the world coincide. There are many coincidences, not all of which are exaggerations. We believe and accept that these beings exist. The majority of people who have seen them say that they are normal beings; and the people who speak of them say that they do not believe in ghosts or spirits. Many people have already seen UFOs. General MacArthur, that Yankee murderer, said with regard to the disappearance of a plane that had struck a strange object: ‘perhaps we – together with the Soviets – will have to make war against an enemy arriving from outside Earth’. But conciliation of this type has its limits.

All the people who say that they have seen extra-terrestrials, UFOs, coincide in the fact that these beings have not frightened them, and that they have made themselves understood, without using an audible language, showing them that they mean no harm. They do not provoke a feeling of alarm, but of serenity. They create sensations of mellowness, suppleness, harmony, reassurance. They do not inspire any fear. They must give off a sense of security by their movements, by their facial demeanour, or in other ways. None among those who have seen them have said ‘I was scared, they frightened me’. On the contrary, they awaken a pleasant sentiment, one of respect. They must emit some sort of rays that cause this sensation, if they do exist. None among those who have seen them has said that they were attacked. They have shown no interest in attacking, violating, stealing, possessing: they have come to observe.

This section in particular reeks of woo-woo. To put it bluntly, the evidence for extraterrestrial UFOs is severely lacking. Additionally, there are other, better, simpler and therefore more likely explanations of these things. There is very clearly a cultural aspect to it. People who claim to have been abducted routinely describe extraterrestrials as looking like whatever TV alien style was popular at the time of their childhood. For some that's big rubbery green monsters, for some its little gray guys with black eyes.

There is also strong indication that it is a cultural phenomenon due to the fact that the majority of sightings happen in the U.S. and the U.K.

https://worldpopulationreview.com/country-rankings/ufo-sightings-by-country

Posadas seems to acknowledge this:

We need to wait for further proof. It is possible that they have appeared, though it is also possible that there has been much fantasising, exaggeration or mystical deductions on the part of those who have seen them. But there is testimony from people who seem thoughtful.

But then immediately turns around and acts like extraterrestrial UFOs are a certainty:

We do not know what form they take, or their number, but they must exist, or else they would not appear like this. There are reasons enough why capitalists would not invent these matters.

This means that they have no need for war, that they do not come to Earth with goals of conquest in mind.

They have no aggressive impulse, they have no need to kill in order to live: they come only to observe.

There is one final critical miss here, in my opinion:

The existence of flying saucers and living beings on other planets is a phenomena that the dialectical conception of history can admit. The most immediate consequence we can draw is that, if these beings do exist, they must have a societal organisation superior to our own. Their appearances are not the effect of bellicose or aggressive sentiments.

This line of thought relies on the earlier premise that extraterrestrials are already here and are peaceful. I think I've sufficiently explained why there is insufficient reason to believe that. But worse is, even if they did exist and are currently peaceful, that still doesn't necessarily prove anything about their economic/political system.

It could be the case that they've only sent recon ships to prepare for invasion, to extract capital value from our planet. It could be the case that they never grew out of feudalism, and their monarch simply finds us entertaining. It could be the case that they are hyper individualistic, using a barter economy with no government, but are long lived enough to make technological progress on an individual level, and there's only a few of them in orbit poking around. I absolutely love science fiction, and I could go on with a million other made up examples that would fit the narrative here, but it's only ever going to be fiction. There needs to be much stronger evidence than what Posadas provided.

I'd be very interested to hear your thoughts on this. Because while I heavily disagree with Posadas, this is still an incredibly interesting topic.

we can only do that in our fiction

At present, yes. The hypothetical is in the future, possibly in one where we've developed interstellar travel and we can be the ones visiting the alien planet.