That outweighs by a billion times---animal liberation is inevitable in the short-term---future lives saved depend on humans and are far greater

We should be more pessimistic when we review how nonhuman animals have fared in the last century. At present around 50 billion animals are raised and killed each year to feed humanity. (Many million animals are used for clothing, product testing, research, and entertainment, but their numbers are insignificant by comparison.) Since World War 2, with the invention of "factory farming," farm animals’ welfare has significantly deteriorated, as they now live in conditions that frustrate their most basic instincts (Singer, 2002, chapter 3). At the same time, we’re probably the only animal on Earth that routinely demonstrates compassion for other species. Such compassion is nearly universal in developed countries but we usually know too little, too late, for deeply ingrained habits, such as diets, to change. If improvements in other public morals were possible without any significant biological change in human nature, then the same should be true for our treatment of nonhuman animals, though it will take some time.

Even without any change in public morals, it seems unlikely we will continue to use animals for very long – at least, nowhere near 50 billion per year. Our most brutal use of animals results not from sadism but from old appetites now satisfied with inefficient technologies that have not fundamentally changed in 10,000 years. Ours is the first century where newer technologies -- plant or in vitro meats, or meat from brainless animals -- could satisfy human appetites for meat more efficiently and safely (Edelman et al, 2005). As these technologies mature and become cheaper, they will likely replace conventional meat. If the use of sentient animals survives much beyond this century, we should be very surprised. This thought is a cure for misanthropy. As long as most humans in the future don't use sentient animals, the vast number of good lives we can create would outweigh any sins humanity has committed or is likely to commit. Even if it takes a century for animal farming to be replaced by vegetarianism (or in vitro meats or brainless farm animals), the century of factory farming would represent around 10^12 miserable life-years. That is one-billionth of the 10^21 animal life-years humanity could save by protecting Earth from asteroids for a billion years. The century of industrialized animal use would thus be the equivalent of a terrible pain that lasts one second in an otherwise happy 100-year life. To accept human extinction now would be like committing suicide to end an unpleasant itch. If human life is extinguished, all known animal life will be extinguished when the Sun enters its Red Giant phase, if not earlier. Despite its current mistreatment of other animals, humanity is the animal kingdom’s best long-term hope for survival.