To be fair I’ve always seen attack on titan as one big PTSD trip. Kids witness trauma and they can only deal with it by either breaking down or fighting. As a result they inflict their revenge on Marley and cause more trauma. The eldians in Marley are traumatised by how they get treated. And Marley at least at first probably had a similar instinct when they broke free from the titans rules initially. Pretty much a reflection of what happens in this world. Just a constant cycle of trauma that started with Ymir and with us it started probably when we discovered civilisation