As you say, we are hairless chimps, and this fact, our common ancestry with chimps, bonobos, and gorillas, has a lot to do with the core of our behavior and feelings. You are impressed with the power of this idea to explain our aggression and violence.
See this, however. I’m an East-African Plains-Ape Cooperator… The link is to a blog post by U C Berkeley Economics Prof. Brad DeLong. Among other things, he is an economic historian, and economists, indeed thinkers since before economics existed such as Hobbes, Locke, and Rousseau, have wondered where our social arrangements come from. Prof. DeLong, in this link, is discussing a new book, The Economics of Star Trek, with its author. He has a series of these video interviews with him. The title of this particular post points out another factor of today’s human behavior that, likely, arises in the distant past of our species.
Our modern closest relatives live in social groups with relative peace between the members of a group, indeed, even cooperation among them, including grooming, baby care, foraging, hunting, and defense. All of this is the subject of Jane Goodall’s, Dian Fosey’s, and other intrepid researchers’ investigations.
Thus within a group, mechanisms exist to establish “pecking order” or social status, priority for food and mating, all usually peacefully, while aggression and fear govern relations between groups.
You point out that Confederate soldiers, volunteers or conscripts, felt that they were defending hearth and home. They were defending those whom they perceived as their group and their social system, which was slavery, whether or not a soldier or his family owned slaves. Of course, Florida’s loyalists, who fought for the Union, also felt that they were defending hearth and home, and their social system as defined by the Constitution of the United States. Northerners and Southern loyalists entered the war to defend the government of the United States against attacks by white Southerners. It was only later that the Northerners’ war aims expanded to include the underlying cause of the conflict. The black slaves who escaped to Union lines and enlisted in the U. S. Army were defending hearth and home against the slavers who had been attacking them and their society and families for more than two centuries.
What moral difference do you see between these three groups of modern day, hairless chimps?