Many families, especially ones with young children, find that dogs are an asset when they are still playful puppies (capable of keeping the children amused), but become an increasing liability as they grow into middle age, with an adult appetite but sans youthful allure. Moreover, there is always a problem of what to do with the animal when they go on holiday. It is often inconvenient or even impossible to take the dog with them, whereas friends tend to resent the imposition, and kennels are expensive and unreliable. Let us suppose that, inspired by Singer's article, people were to hit on the idea of having their pets painlessly put down at the start of each holiday (as some pet owners already do), acquiring new ones upon their return. Suppose, indeed, that a company grows up, 'Disposapup Ltd.', which rears the animals, house-trains them, supplies them to any willing purchaser, takes them back, exterminates them and supplies replacements, on demand. It is clear, is it not, that there can, for Singer, be absolutely nothing directly wrong with such a practice. Every puppy has, we may assume, an extremely happy, albeit brief, life—and indeed, would not have existed at all but for the practice. Yet the activities of the company and its clients would, I imagine, cause a general outcry amongst animal lovers.
(Michael Lockwood, "Singer on Killing and the Preference for Life," Inquiry 22 [summer 1979]: 157-70, at 168)
Note from KBJ: There are two replies Singer can make to this objection. First, he can deny that his theory (preference utilitarianism) has the stated implication. This is called grasping the bull by the horn. Second, he can admit that his theory has the stated implication, but accept it. This is called biting the bullet.