I think another point to add is that raising animals for food can be seen as a symbiotic relationship.
If not for the development of animal husbandry, would pigs, chickens, and such be as successful (from a total population pov)? I think not. Many animals have the chance to be alive, only because they are supported by humans. This relationship is not only one-way: they are protected from predators, sheltered, and fed.
Of course this doesn't justify mistreatment. But it puts in perspective the idea that turning vegetarian, and banning meat would be good for those animals in question. It wouldn't: they wouldn't be alive in the first place.
By the way, even animal husbandry is not specific to humans. Ants for example, have "farmed" aphids for millions of years. They milk them for honeydew and eventually eat them.