No one in the habit of eating an animal can be completely without bias in judging whether the conditions in which that animal is reared caused suffering. The people who profit by exploiting large numbers of animals do not need our approval. They need our money. The purchase of the corpses of the animals they rear is the only support the factory farmers ask from the public. Hence the need for each one of us to stop buying the produce of modern animal farming - even if we are not convinced that it would be wrong to eat animals that have lived pleasantly and died painlessly.
Vegetarianism is a form of boycott.
For most vegetarians the boycott is a permanent one, since once they have broken away from flesh-eating habits they can no longer approve of slaughtering animals in order to satisfy the trivial desires of their palates. But the moral obligation to boycott the meat available in butcher shops and supermarkets is just as inescapable for those who disapprove only of inflicting suffering, and not of killing. In recent years Americans have boycotted lettuce and grapes because the system under which those particular lettuces and grapes had been produced exploited farm laborers, not because lettuce and grapes can never be produced without exploitation. The same line of reasoning leads to boycotting meat. Until we boycott meat we are, each one of us, contributing to the continued existence, prosperity, and growth of factory farming and all the other cruel practices used in rearing animals for food.