I agree. I don't eat beef/chicken/pork for environmental reasons. Such a waste. I think what the article is suggesting is that the developing world (no necessarily the US) is in the most need of protein. You seem like you know a lot about nutrition, so i'd love to hear your thoughts on the FAO study.
Here is an excerpt from the study:
"It is widely accepted that by 2050 the world will host 9 billion people. To accommodate this number, current food production will need to almost double. Land is scarce and expanding the area devoted to farming is rarely a viable or sustainable option. Oceans are over-fished and climate change and related water shortages could have profound implications for food production. To meet the food and nutrition challenges of today – there are nearly 1 billion chronically hungry people worldwide – and tomorrow, what we eat and how we produce it needs to be re-evaluated. Inefficiencies need to be rectified and food waste reduced. We need to find new ways of growing food."