Selecting Anarchism as an example, it defends a state of affairs without coercion or oppression, and it also defends, at least from what I read, the abolishment of prisons. What would one do with the supposed insurgents or people who want to govern the others? They would naturally arise because I think it's part of the animal nature of man to want something for himself and defend it, be it in groups or not? There would be people against the new system of things. So is it possible to live in a world without any oppression or authoritarianism? I believe it's an utopia.
What would one do with the supposed insurgents or people who want to govern the others?
1) Both Anarchism and Communism aim for the abolishment of classes, so that there will not be profit generated from human-to-human exploitation. In that sense, people of a classless society will not have the incentive to rule, as they will have nothing to gain from it. In the extreme case, that there are certain people/groups of people that won't leave their ruling positions, wish to remain in the ruling class or seek to have a ruling role for psychological reasons, they will be cast out from this society naturally.
2) Even in an anarchist society it still exists some form of "punishment", but certainly not suspending the freedom of the others, but more focusing on compulsory work for the society. Mainly, anarchists argue against prison system in the existing capitalistic system, which is used not only to protect the society against crimes, but as a political tool in the hands of the ruling class to express and maintain their dominance.
I think it's part of the animal nature of man to want something for himself and defend it
That's just opinion-based, not a scientific fact.
So is it possible to live in a world without any oppression or authoritarianism? I believe it's an utopia.
It is possible if the elements that cause oppression are removed. Historically, as an example, you can check the revolution of Slaves/Spartacus, the American revolution, the French revolution, etc.
A map of the world that does not include Utopia is not worth even glancing at. Oscar Wilde
In the Spainish Civil War there existed some of the largest groups ever calling themselves anarchist. They fought effectively against both political incursion of nominal allies and military incursion of enemies for a few years before being disarmed and destroyed.
I understand executions of traitors and spies was not uncommon.
They wouldn't cohesively do anything because they would need to establish a formal hierarchy in order to act as a singular entity against a unified opponent. Anarchists don't believe in the establishment nor perpetuation of hierarchies and therefore they'd simply roll over one-by-one when confronted by an external threat. Not only this, the anarchist cannot ideologically understand such a thing as the existence of externality / internality would construct a formal hierarchy that is, itself, incompatible with the ideology.
TLDR: anarchism is incoherent.
In agreement with koita-pisw-sou. Another view is anti-hierarchy not anti-structure. A society of highly educated, collectivist-minded people for example could design horizontal voting systems for policy. Education and social services, would be a worthy start in "de-programming" people from antisocial aggression related to manufactured scarcity. The "ideal" could take generations to get to, and would also be a shift in culture.