It's almost certainly true for some vegetables, but I'm not sure any of those crops account for a majority of a vegetarian diet. Soybean, corn, potatoes, rice

It's almost certainly true for some vegetables, but I'm not sure any of those crops account for a majority of a vegetarian diet. Soybean, corn, potatoes, rice and wheat are like, really awesome. But "let's not use any animal products at all" is a much harder sell. "Hey, if you eat mostly chicken and pork with just the occasional steak or burger on a special occasion you can get like 50%+ of the environmental benefits" is a much more plausible way forward for the US.