The argument of demand and supply is not a valid one. On this planet, a great number of human beings (Two thousand per day according to a newspaper report) and countless animals are killed by motor vehicles everyday. Just by driving vehicles or even sitting in them, we are encouraging the motor industry to make more motor vehicles. If we use the demand and supply argument, then just by using motor vehicles we are encouraging the killing of countless animals and a great number of human beings on the roads everyday — which is worse than eating meat! It is true that we are indirectly involved in the killing of animals but, as explained, there is no kamma-vipaka of killing. This indirect involvement in killing is true whether we eat meat or not, and is something which is unavoidable.
We encourage killing even when we eat vegetarian food. Every day monkeys, squirrels, foxes, flying foxes, and other destructive pests are killed because they eat from fruit trees planted by farmers. Vegetable farmers also kill caterpillars, snails, worms, grasshoppers, ants, and other insects, etc.. Similarly, in Australia for example, kangaroos and rabbits are killed every day because they eat the crops. Many items commonly used by just about everybody cost the lives of living beings. For example, silk is made at the expense of the lives of countless silkworms, and white shellac (used to manufacture many products, including food), of countless lac insects. Cosmetics contain a huge range of animal derived substances. Many food additives, e.g. colourings, flavourings, sweeteners, also use animal derived substances. Commercially produced cheese uses rennet which is extracted from calves’ stomach to make the milk coagulate. Leather and fur are of course made from the hides of animals, often slaughtered for this purpose. Photographic film uses gelatin which is obtained by boiling the skins, tendons, and bones of animals. Even fertilizers for the vegetables and fruit trees often include dried, ground fish bones, and other fish scraps. Also, the use of cow’s milk and honey involve much cruelty to the animals or insects concerned. All these go to show that it is very difficult not to be involved one way or another in the cruelty inflicted on animals. So if one does become a vegetarian, one should reflect on the above and refrain from being over-critical of those who eat meat.