To be fair, pasture raised is more expensive, so people would eat less beef. I don't think it's fair to talk about scaling current consumption.

You say that, but it's not really just about grass-feeding. Cows are already fed almost 90% inedible crop materials that would be getting disposed of anyway. We could be doing better, but cattle's food source is sorta the wrong focus.

And as much methane is in manure, it's better for the environment (including GHG) than synthetic fertilizers.

The real answer is changing our meat/vegetable balance AND improve the process AND continue to improve humane regulations (and those 3 goals often synergize with each other).

I hate to be "that guy", but I feel like none of your references are really properly rebutting his valid point. "We don't eat cats and dogs" is a common anti-balanced-diet dogwhistle that tries to touch on heartstrings instead of logic or even ethical behavior. You might not have meant it that way, but he was justified in pointing out the cultural bias of it.

And "cultural imperialism" is different from "literal imperialism", but that also means your rebuttal was a gishgallop, changing the topic. I'm ASSUMING you didn't mean to secretly change the topic to prevent losing on that previous point, but that's what the reply looks like anyway.

It's not that it's not possible, it's that it's so easy for the layperson to fuck up. Both those claims about low diabetes risks and being able to supplement missing micronutrients are true alone, but mix them together and you get a risky balance that needs careful tracking.

You're basically required to eat a cup of cashews a day and put nutritional yeast in at least one meal. If you deviate from this you're going to be at risk of malnutrition.

Otherwise you're going to be opting for fortified foods like bread, rice, salt, cereal, etc. Which again have all good choices within them but if you deviate from the recommended track (wheat bread, bran cereal, etc) then without close tracking you're most likely either eating too little risking malnutrition or you're eating too many carbs to compensate and spiking your blood sugar

Also there's several concerns of using fortified foods as your main source of micronutrients. Mostly that fortified foods don't fully replace the nutrition of whole foods, and the upper levels of these supplements aren't well controlled leading to a risk of toxicity. Stand-alone supplements are a better alternative, but do have a cost associated with them.

You can totally do vegan, and do it right, but you're never going to recommend it to Debby down the street who packs her kids lunches every day without also recommending she starts her family on a multivitamin. It's just not scalable to the whole population like that.

https://pubmed.ncbi.nlm.nih.gov/27886704

Vegans need reliable sources of vitamin B-12, such as fortified foods or supplements.

https://pubmed.ncbi.nlm.nih.gov/21139125/

Vegetarians exhibit a wide diversity of dietary practices, often described by what is omitted from their diet. When a vegetarian diet is appropriately planned and includes fortified foods, it can be nutritionally adequate for adults and children and can promote health and lower the risk of major chronic diseases. The nutrients of concern in the diet of vegetarians include vitamin B(12), vitamin D, ω-3 fatty acids, calcium, iron, and zinc. Although a vegetarian diet can meet current recommendations for all of these nutrients, the use of supplements and fortified foods provides a useful shield against deficiency. A vegetarian diet usually provides a low intake of saturated fat and cholesterol and a high intake of dietary fiber and many health-promoting phytochemicals. This is achieved by an increased consumption of fruits, vegetables, whole-grains, legumes, nuts, and various soy products. As a result of these factors, vegetarians typically have lower body mass index, serum total and low-density lipoprotein cholesterol levels, and blood pressure; reduced rates of death from ischemic heart disease; and decreased incidence of hypertension, stroke, type 2 diabetes, and certain cancers than do nonvegetarians.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8066912/

Despite the enormous benefits of food fortification strategies on nutritional status, some studies have identified opposite results in terms of no impact of food fortification programs and of guaranteeing safe upper limits. For example, a study conducted among Brazilian children under the age of six found no effect of iron-fortified flour on anemia prevalence. The study consisted of four population-based surveys conducted over a four-year period, and it measured dietary intake and hemoglobin levels. The findings showed an unexpected increase in anemia among children. Despite the average intake of fortified flour detected by the study amounting to 100 g per day, the poor diets quality of children with low bioavailability of iron compromised the benefits of fortified flour

Also from your article:

Vegetarians and vegans are at reduced risk of certain health conditions, including ischemic heart disease, type 2 diabetes, hypertension, certain types of cancer, and obesity.

While the diet supports it, this is just as much a correlation. It does not account for the other lifestyle choices of vegans and vegetarians such as exercising more often than the typical person.