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As they are, and, let's say, without the ability to avoid military actions, but with the option to defect (that is, betray, and not be born there) to the camp of any representative of the parties involved in this conflict, at will.

Ugh, I would sell my own mother for the chance to see Stalin on a stake, and the Mausoleum on fire.

Added 15 minutes ago

Judge for yourself - I, like many, was raised on Hollywood movies, where tolerance and love were the main values, especially love - the hero who pursued love was always rewarded, without exception.

This is a significant problem, especially when we are talking about the seventeenth century.

Andrei, who sincerely loves and saves his beloved from starvation, is shown to us as a negative character and dies.

Not at all. I don't remember the movie, but in the book there is no hint of the author's dislike for Andriy. He only describes the Poles negatively. He treats the Jews with condescending pity, I would say. First of all, Andriy is a man ahead of his time, and naturally suffers for it.

and the teacher says that he is acting correctly...

He is an exemplary, idealized hero within the framework of his era. Gogol clearly sympathized with the Zaporozhians, and all the traits he attributed to them, he put into the image of Taras, only in a somewhat exaggerated form.

and it is he who is the main positive hero, not a traitor

Ostap, strictly speaking, is not a hero at all and appears only a few times. He is a functional character, he is needed for contrast with Andriy - one, to die heroically and move the plot forward - two.

"yes, you have more of a noble appearance. you were never one of us"

Not at all. In fact, the Cossacks, like the казаки, considered themselves almost knights (meaning: a noble cavalryman, and in their case, this is even 2/3 true) and certainly not commoners. It was unthinkable to compare a Cossack with a peasant, a serf.

Added 1 minute ago

He fights because he loves to fight. The ataman of the Cossacks made peace with everyone, but Taras found life boring and called on everyone to go and destroy the Poles and Jews, for the Orthodox faith.

That's right. Patriotism has nothing to do with it. Taras doesn't even have his own sovereign state.

Added 2 minutes ago
Oh, and in the movie, the brothers are shown as healthy guys over 20, but in the book, Andriy is 17 years old. And then a lot of things fall into place.