I foresee a day, perhaps not far in the future, in which it is illegal to raise cows, pigs, and other animals for food. The ground for this will not be animal welfare, as you might expect, but environmentalism. Lawmakers, perhaps as a result of an international treaty, will prohibit the intensive rearing of at least large hoofed animals for food, on the ground that it is damaging to the natural environment. It will be said that animal husbandry is one of the most inefficient and destructive industries on the planet, and that the planet cannot survive unless humans change their diets. Since diets change only slowly, if at all, it will be thought justifiable to coerce people into changing.
I object to this for two reasons, one conditional and one unconditional. First, the ground is improper. The natural environment, unlike individual animals, is inanimate, unconscious, and insentient. This is not to say that we may do whatever we please to the environment. Obviously, if the environment is polluted, then everything that depends on the environment is adversely affected. But the environment has no intrinsic value; it is valuable only for the sake of sentient beings who depend on it. It has, in other words, extrinsic or instrumental value only. Individual animals, qua sentient beings, have intrinsic value. They are valuable for their own sakes, not merely because they are valued by (or useful to) others. So if animal husbandry is to be prohibited, it should be on animal-welfare grounds, not environmental grounds.
My second objection, unlike the first, is unconditional, and therefore more sweeping. It is that coercion (via legal prohibition) is not a proper method of protecting animals, at least if the aim is to protect animals. The reason is that it has a backlash effect. The best thing that one can do for animals, in the long run, is to persuade people to stop eating them. Of all the ways of influencing behavior, rational persuasion is the most effective, the most secure (in the sense of long-lasting), and the most defensible from a moral point of view. Force, coercion, and manipulation, by comparison, are inferior on each score.
I believe that as time passes, humans will, for various reasons, change their diets. Some will reduce their consumption of meat for the sake of the animals. Others will do so for the sake of the environment. Others will do so for health reasons. Still others will do so because they believe, rightly or wrongly, that vegetarianism (or demi-vegetarianism) is good for human beings. Nobody will be forced, coerced, or manipulated, so nobody can complain about being disrespected.