In reverse order:
Americans tend to eat only prime cuts. Just like with dogs, it's far healthier to eat the whole animal over time, plus the effect of red meat on cholesterol depends on how it's raised. I don't have studies on hand but pasture-raised animals are not only lower in the factors that tend to raise LDL, but they also are higher in factors that either support HDL or lower LDL.
I won't argue that a vegetarian lifestyle is healthier - of course it is. But it's not for everyone. It's an expensive lifestyle unless you are resigned to great lack of variety such as is faced in a subsistence lifestyle (and that lack of variety is unhealthy for growing kids). Animal products are a much cheaper and more nutritionally complete source of energy as a supplement to a basic cereal diet. Not huge chunks of meat like we Americans eat without blinking. My best friend was Japanese and I picked up her family's sensible moderation of meat consumption.
It does take more acreage to grow the amount of legumes, oilseeds, and grains required to feed a family of four, versus a cow/calf unit. Not to mention a small flock of sheep, which can use (and IMPROVE) land which is unsuitable for anything else. And those acreages involve tillage, which increase greenhouse gasses.
The science behind carbon fixing is firm and well-documented among agriculturalists. It's something we have to take into account - I live and breathe organic matter - I dream of more and spend all my time hoarding it and scheming of ways to increase it in my soil. Grasses and forbs (ie, pasture plants) intake carbon at a tremendous rate. The carbon is transferred to the roots for the sake of growth. My sheep eat the tops of the plants, and the roots die back, decomposing into rich organic matter and transferring the carbon directly to the soil. Soil rich in carbon can now fix nitrogen more easily, and also encourages the population of soil organisms, both macrobiology like earthworms, and also microorganisms like the anaerobic bacteria required for - guess what - root function!
Roots require these bacteria to uptake minerals from the soil. Without them, the plants grown in these environments (such as grains, legumes, and vegetables grown in commercial operations) are low in mineral content.
Commercial row crop operations make up for these deficiencies by shipping in soil conditioners - whether "organic" or chemical - but they cannot make up for the double whammy of the tilling of the soil, releasing carbon into the atmosphere, and soil nutrient depletion. You can't just "put it back." It's a cycle that takes far more than a single growing season to reestablish.
Bill's point is not to make a scientific statement. It is to raise questions about the validity of valuing an ideal meatless society when the assumptions which such a model makes are based on the idea that all meat is raised or must be raised in confinement operations. Our hope and dream is that confinement operations (ie, concentration camps for animals) go the way of Auschwitz very soon.
But that won't happen by trying to get Americans to ditch meat eating. Instead a more constructive approach, which Bill wants to emphasize, is for Americans to rethink their consumption of meat at all levels. Ask for naturally raised meat. Support local farmers. Consider the "whole animal" approach to consumption and moderation.
A single calf SHOULD be able to support a family of four for a year. But not if you only want to eat steak, and 14 oz at a time. Do the math. Compare to current reported stock levels. There's SO much waste in the beef processing industry because Americans are ridiculously picky. Ditto any other livestock. Ironically, raising a quarter of the livestock, farmers would earn far more for many reasons. All the middle men eat up their profits currently (speaking of cow/calf operations). Transportation is a nightmare.
Less time simply handling stock means more time spent putting in improvements that increase the sustainability, efficiency, and profitability of their operations (conservation-oriented pasture divisions, erosion control, watering systems that retain waste and filter fresh water back in).
I have a friend who used to do contract work for the feedlots - her job was to take calves that weaned too light or unhealthy to withstand life in the lots (!), and be sort of a halfway house. She fed concentrates (locally sourced feeds, mostly waste from mills or vegetable packing plants), but the cattle stayed on pasture. Twice a day she'd use her horse and dogs to push the cattle up to the bunks, to teach them to look for feed there.
It was a pretty awful life. They had to be ready any minute to jump up and unload a truck that came in with another 80 head or so of calves, and sort them and check them for injuries and illness. Trucks might pull in at 2 am, 4 am, in any weather, Christmas, someone's birthday, with no warning. Someone always had to be there so no family vacations. It was rough. The calves had never seen dogs, or each other for that matter, and only spent maximum of six weeks there. So just as she'd get a lot working safely and nicely, they'd be gone and replaced with another lot of troublemakers.
Last year their mom, who owned the farm, passed away and left it to them, along with a very hefty inheritance. First they went on a LONG vacation!! Then she went on another one out west to see high-sustainability cattle operations and get some ideas to bring home and put into effect. They spent about $75,000 cash on redoing their fences, with the help of the water and soil conservation people, so that the cattle didn't lounge in the trees and tear them up, and putting in automatic waterers with recyclers so they didn't need access to bodies of water or any watersheds.
She went to about 75% grass-based and put calves of her very own, in. The first ones will be ready in April. She's also getting a processor license and is planning to offer fresh-off-the-farm cuts. She lives only about an hour from three major NC metro areas.
Here's an example of just one person who converted her whole system and will easily be able to provide meat with a minimal impact on the environment. She's just one. Eventually she'll be able to stock about 500 head of cattle and about 50 goats to follow behind and reduce parasitic load on the pasture. She can feed 2000 people. She's got about 100 neighbors with similar sized farms, within a ten-mile-radius. Most of them run confinement chicken operations, like they did before they went to the cattle. The life of the chicken farmer is even more awful than the contract cattle farmer, except the risk of injury is lower.
It's not about studies and data - it's about knowing the facts about the business and culture before making assumptions. Take methane production. There's much data about how much, etc, but there IS no data that I know of, comparing offsets, whether current or potential, of beneficial processes created by pasture-based livestock farming. Just offhand, consider the wild state of the North American continent before European settlement. There were 100 million bison alone - exactly the same number as cattle today, and bison are HUGE - twice to three times the size of cattle. This is not to mention the many million pronghorn antelope, plus dozens of other large to medium sized ruminant species that today are gone or greatly reduced.
It's true Bill is speculating, that's the nature of a blog. I just wanted to show there's more layers raised by this issue than people may think of, who aren't intimate with the agricultural scene.