I consciously avoided any reference to ethics to avoid that quagmire. But unlike ethics and the effects of the complex series of compounds that are food on the complex system of tissue that is the body, the environmental economics of food are pretty much straightforward and as far as I can tell both well understood and lacking the ridiculous back-and-forth of nutritionism.

It's absolutely possible that many vegans are vegans due to some psychological pressure towards purity or ascetism, and they just coincidentally chose a pressure vent that also makes sense in an economic and environmental sense. I'm sure many of them might even be aware of that dualism.