Please let me know if this community is not the best place for this post.
When I was a teenager, and even in my twenties, I used to be quite idealistic, naive, and somewhat radical, believing that all humans have the capacity to be good, and that the only thing preventing utopia where all live in abundance were the historical shackles of national/cultural/religious identities. As in, humans would for sure all get along, if only there were no major reasons for any "us vs them" type thinking.
But the older I get, the more my thoughts on the topic have shifted. My idealism has constantly been worn down by finding out about more and more people who would be happy to fuck over every single other person on this planet if it meant they could get a bit further "ahead" than everybody else. But even on a much smaller scale, after establishing my own family and building my home, at some point I realised that I would personally also be willing to go to extreme lengths if necessary to protect the way of life of my loved ones, including picking up a gun if our neighbouring country decides we should no longer have our freedom - this is something I would have considered "idiotic patriotism" when I was younger. Basically, this means I would also be willing to fuck up the lives of others in order to improve the lives of my family, and I think the same is true for most people.
What I'm getting at is that I think there are lots of reasons that people can have to hurt other humans, ranging from psychotic greed to a strong commitment to close ones. I think this is just human nature. I'm using the word "hurt" here in a very broad sense, including taking advantage of somebody, etc.
If indeed this is human nature, and humans are willing to exploit others to try and improve the situation for themselves and their loved ones, how can communism work? Would we not need to "evolve" to a new stage of humanity first, where people are capable of putting the needs of society above their own desires?
I apologise if this is a dumb question with some obvious answer, I admit I have not read any books on communism and am probably missing some key points.
Even if you accept that human nature means people want to exploit each other (which is contentious), the point of communism isn't to change that. It's to structure society so that those who would be exploited and are exploited have the power. If the people who want to exploit others don't have armies or wealth or positions of power, then they can't do much. Communism tackles this by placing those who are exploited for their labor in power. Because labor is how society exists. It's how the buildings get made, it's how the heat stays on, it's how we get food and water and antibiotics. This grounds the idea of exploitation in a material relationship with the mode of production. It avoids the moralism of seeing exploitation as some inherit demonic influence on mankind. People exploit people because it betters their own lifestyle and because society is structured to allow those people power.
Think of Marx and other revolutionary science the same way you would think about physics or other science. In the late 1800s science began formalizing and moving away from the Enlightenment philosophies. Also at this time the industrial revolution had taken hold and was creating a new abstraction for feudal exploitation. So just like how the modern physicists began to move past Newtonian physics, social scientists began moving past the old ideas about human nature and society. This means dispelling a lot of old superstitions about people's places in society.
In that we consider the situation you describe. You're a peaceful and successful socialist/communist country but your neighbor decides to invade just because they don't like you. Well, people don't act for no reason. In history a country invades another for resources or to defend its own political position of power. They may say they fight for honor or freedom or God, but those are just flimsy justifications that obscure the material reasons for conflict. So your communist nation would have to be smart enough to understand that and work to decipher what's really going on so you can solve the problem.
Under communism you use an inductive system that moves between practice and theory to solve problems. So you come up with a reason why you think your neighboring country might invade, and then you test it by diplomacy or war. You see what doesn't work and you go back and adjust the theory. Then you test it again. It's literally a scientific method of social organization.
One of the reasons why capitalism is so precarious is that it contains what are called contradictions. Contradictions are not logical contradictions. They are two things that oppose each other but also can't exist without the other. The buyer and the seller for example. The buyer wants the cheapest price and the seller wants the highest price. If there are no buyers there are no sellers. These contradictions exist all over capitalism and go unaddressed because the wealthy refuse to recognize them. They don't have a scientific view of society. They use mystical explanations for these contradictions and the crisis to which they lead.
Under communism there will also be contradictions. They will be different from those of capitalism but they will exist nonetheless. It's up to a communist society to recognize their own contradictions and resolve them before they cause crisis. Communism doesn't aim to be perfect or eternal, it just aims to do better for everyone.
Thank you for the detailed answer, but it created a lot of new questions for me. I think the most important one is the question of how communist society can react to conflict and "evil" without a state.
I get the impression from your answer that in communism, having a military is possible:
Also, from these statements, I gather that it's possible under communism to actually limit somebody trying to seize power or just effectively start doing "organised crime":
But how is it possible to have a military or to limit unjust behavior within society if there is no state?
I don't think you can do it without a state. That's where I differ from my anarchist comrades. In the beginning and for some time you will need a state. But the state doesn't have to be organized as it is today.
Back to communism and revolution being a social science -- you have to be careful with speculation. We can try to sit here and figure out what that society would look like down to the fine details but we won't actually know until it's accomplished. It's a bit like people trying to predict iphones when computers were the size of rooms. You can kinda see what might happen and what might be possible but the exact outcome is unknown. There could be a stateless solution that I can't imagine because I spent my whole life and my whole historical understanding includes various state entities. Or, as I suspect, there must be a state for some time before something stateless comes along. Regardless, it's important to remember that these organizations of society are always changing and will always change. A communist state will not be eternal and a stateless society will also not be eternal. They will each contain contradictions and must be addressed when they actually exist. Contradictions lead to instability.
To re-frame the problem, history is a struggle between classes. If you want to look at it like a struggle between those who exploit and those who are exploited, you can. So even in a communist state or a stateless society, those who exploit will still exist. Right now it seems the only solution to stopping those people is a military or police force of some kind. I don't know the exact shape of that. I just know that the American version of policing and military is not the default option and it's not the only viable option. It's hard for people who live under capitalism and who look at capitalist history to see alternatives. It's purposefully presented as if the current organization of society was inevitable and the most efficient/stable outcome. But it's not.
This goes into the popular conceptualization of human nature. If you're a scientist, you try to be objective. When you study something you compare it to something else, some kind of neutral control. But capitalist sociologist, psychologists, and economists focus solely on society under capitalism. Then they draw conclusions about all of human nature from that. Capitalism is just one outcome just as feudalism was one and slavery before that. It's not even the only form of organization in history let alone the world and all of humanity. So how can we talk about human nature when we don't study all of human nature? And this is a common thing you'll see in academic studies under capitalism. When they do study other forms of society, they'll use the underpinnings of their field, which is founded on studying capitalist society, as the assumptions from which to draw conclusions. So they end up being biased.
We also can look at the history of science in the West to gain an understanding. Under late feudal and monarchist states, they began trying to use data to govern. They would collect data about the far-off places of their empire and use that information to make decisions. Then you get into the industrial revolution. People are forced from self-driven artisan labor into factory work. The factory work is miserable and bad for their health. People begin to refuse to work. They become vagrants. The capitalist states notice this through their data collection. In order to account for why so many people are miserable and/or not working they come up with medical reasons. They open asylums and sanitariums. They diagnose people as mentally unwell and force them into padded rooms. This separates them from the rest of society. They make laws against vagrancy and jail them too. Then they force them to work at gunpoint.
So the early history of sociology and psychology in the West is one of capitalism trying to hand-wave away its faults. It's a mystification of the problems of the society rather than address them. Because addressing them means not having factories and that means capitalists lose money and status. It's not that there aren't truly mentally ill people or criminals, it's that the basic malaise created by the mode of production is pathologized and criminalized.
As you can probably tell by now there are a couple of things you can do to better understand communism. One is to study history, the real history, of the world. There is the mystical version of history where the context of production is ignored and many things are hand-waved away in favor of a nice story. Another is to read the experiences and thoughts of revolutionaries. They were the ones carrying out the experimentation of the social science. They were the ones putting theory to the test. Communist revolutionaries also tend to be big writers so they have journals, essays, and entire books on what they were doing and why. Lenin, Stalin, Mao, Castro, etc all have writings. You can also read the theory too, so Marx, Engels, etc.
Of course the big names aren't the only ones. There is a long and rich history of people trying to solve these questions you ask.
https://www.marxists.org/archive/index.htm