Over the last few years I've seen debates among EA community members over whether one's economic choices as a vegetarian have any effect on the supply of animal meat produced in industry. This has always perplexed me, as Will MacAskill wrote in Doing Good Better about the mechanism by which vegetarianism is thought to decrease the supply of meat products. While one may agree or disagree with the claims Will makes, this excerpt can provide the grounds framing the discussion.
Consider ethical consumption, like switching to fair-trade coffee, or reducing how much meat you buy. Suppose someone stops buying chicken breasts, instead choosing vegetarian options, in order to reduce the amount of animal suffering on factory farms. Does that person make a difference? YOu might think not. If one person decides against buying chicken breast one day but the rest of the meat eaters on the planet continue to buy chicken, how could that possibly affect how many chickens are killed for human consumption? When a supermarket decides how much chicken to buy, they don’t care that one fewer breast was purchased on a given day. However, if thousands or millions of people stopped buying chicken breasts, the number of chickens raised for food would decrease--supply would fall to meet demand. But then we’re left with a paradox: individuals can’t make a difference, but millions of individuals do. But the actions of millions of people are just the sum of the actions of many individual people. Moreover, an iron law of economics is that, in a well-functioning market, if demand for a product decreases, the quantity of the product that’s supplied decreases. How, then, can we reconcile these thoughts?
The answer lies with expected value. If you decline to buy some chicken breast, then most of the time you’ll make no difference: the supermarket will buy the same amount of chicken in the future. Sometimes, however, you will make a difference. Occasionally, the manager of the store will assess the number of chicken breasts bought by consumers and decide to decrease their intake of stock, even though they wouldn’t have done so had the number of chicken breasts bought by consumers and decide to decrease their intake of stock, even though they wouldn’t have done so had the number of chicken breasts been one higher. (Perhaps they follow a rule like: “If fewer than five thousand chicken breasts were bought this month, decrease stock intake.”) And when the manager does decide to decrease their stock intake, they will decrease stock by a large amount. Perhaps your decision against purchasing chicken breast will have an effect on the supermarket only one in a thousand times, but in that one time, the store manager will decide to purchase approximately one thousand fewer chicken breasts.
This isn’t just a theoretical argument. Economists have studies this issue and worked out how, on average, a consumer affects the number of animal products supplied by declining to buy that product. They estimate, on average, if you give up one egg, total production ultimately fassl by 0.91 eggs; if you give up one gallon of milk, total production falls by 0.56 gallons. Other products are somewhere in between: economists estimate if you give up one pound of beef, beef production falls by 0.68 pounds; if you give up one pound of pork, production ultimately falls by 0.74 pounds; if you give up one pound of chicken, production ultimately falls by 0.76 pounds.
MacAskill, William, Ph.D. "Why Voting Is Like Donating Thousands of Dollars to Charity." In Doing Good Better: How Effective Altruism Can Help You Make A Difference, 87-88. New York, NY: Penguin Random House LLC, 2015.
The economic impact of vegetarianism or veganism is only one factor in the decision of whether one should become a vegetarian or vegan, but an important one. Further discussion of why to become vegetarian on economic grounds within the community can be found here.