The point that many grass-animal advocates ignore is the net life-systems benefits of shrinking the footprint of livestock-based grazing operations--even small-scale ones.
For example, ONE THIRD an acre of land (using small scale responsible disturbance/tillage) can produce about 240 pounds of organic soybeans (that's 27,840 grams of protein), which is over 20 month's worth of the entire protein needs of one person, presuming 45g/protein per day.
The area needed to produce the same amount of milk or meat (and let’s presume there's no grain/tillage supplement) is far larger, depending on many factors. So the ability to re-wild all grazing/haying land and focus on growing food over smaller tillage/disturbance areas for human consumption, would provide a far larger net gain in LIFE systems, than would shifting to all-grass grazing meat production.
Old hayfields and pastures could be planted with perennial crops. We could reduce total tillage ag by 75% simply by no longer keeping livestock that rely on grain crops. Plus we would restore valuable habitat for wildlife currently displaced by tillage, haying, and grazing.
SOYBEANS: 116g protein/pound
GRASS-FED COW 117g protein/pound
SOYBEANS: 1/3 acre=27,840 grams per protein
GRASS-FED COW 1/3 acre =14,152g protein presuming 1.8 acres of pasture needed per rotationally-grazed cow (likely is more--anyone have good numbers?)