Environmental science aside, morally, ethically, and from a purely sustainable engineering standpoint, the fact that each year, 10 billion chickens, cows, pigs, sheep, are living in windowless sheds, wire cages, gestation crates, veal crates, and other confinement systems in US factory farms and are then slaughtered for food, eventually has to be reckoned with. When folks select a package of meat at the store, there needs to finally be a conscious connection to the concrete reality of how it got there - the road to the shelf runs straight through the slaughterhouse.
Cows raised for beef spend their existence in packed feedlots, never shielded from cold, rain, and snow, freezing wind, or blistering heat. Dairy cows spend their days in "dry-lot" dairies, confined to cramped stalls; if they are kept outside, they are crowded in pens, sometimes forced to stand and lie on feces and urine-caked soil. The industry artificially inseminates the females to keep them pregnant in order to continually produce milk. As soon as they are born, male calves are sold for beef production. Others are sold to veal producers, where they are chained and held in tiny, wood crates and fed a liquid diet (all to keep their flesh soft and pale). The real sound of our cruelty is voiced by the mothers, who will search and bellow for their calves long after they have been taken away (calves are taken immediately after birth).