Arguments about tribal societies, third-world countries, poor areas, and so on, don't apply very well in first-world countries like the United States. The majority of Americans could easily handle major diet changes, if they had the will. You see this happen when people, wherever they live in the US, are advised by doctors to switch to eating less red meat, etc. From the perspective of environmental impact and general scope, tribal societies and extremely poor pockets of first-world countries are a tiny minority that aren't being thought of when people write articles advising more ethical diets. It's an interesting note, but they are exceptions to the rules that apply to most people who read such articles as this.