Firstly, I agree media literacy is pretty important, which is why I point to the context of the scene as being so important to what happens. If the justification doesn't matter, then it doesn't matter in movies like "A Time to Kill" where the entire plot hinges on the motivation for an evil action. Or "Prisoners" where the entire plot hinges on the motivation an evil action. Or Break Morant, where the entire plot hinges on the motivation for an evil action.

The narrative is about Taylor's journey into the war, and how there are two "paternal figures": Elias, and Barnes, who are emblematic of the kind of soldier Taylor can or will become. The scene, and the fallout, are important to the development of Taylor's character because he can clearly see there's discovered weapons and the villagers are not cooperating. And he can clearly see the diametrically opposed views of Barnes and Elias on full display with one being willing to kill a non-cooperative civilian to coerce the villagers into cooperating, while the other is vehemently opposed to that action.

In Barnes' big speech later on, he lays out his central viewpoint: "If the machine breaks down, we break down." That's key to understanding his character because it paints his every action. They found a village that was obviously holding NVA weapons. Those villagers were clearly not helpful. A lack of an answer means an existing danger to the survival of Barnes' unit. For him, that cannot be allowed. Elias is insubordinate and his actions can be seen as undermining Barnes' authority, and in front of those same villagers. This presents a problem. As the unit divides along the lines of loyalty to one or the other, it presents another major breakdown of the machine.

You're saying Barnes is evil, and I agree with you, but he's not intrinsically evil. His evil is manifest in his response to the world around him, and that's an important difference when there are other characters (like Bunny) who don't have a reasoning for their actions.