The sentiment to which [the utilitarian] appeals is generalized benevolence, that is, the disposition to seek happiness, or...good consequences, for … - J. J. C. Smart

Certainly there would be no future suffering on earth if all life on earth ceased. But most people seem glad that they were born: we do not usually think of present people (and animals) that the pain in their lives outweighs their pleasures...There have been great advances in the human condition due to science: recollect the horrors of childbirth, surgical operations, even of having a tooth out, a hundred years ago. If the human race is not extinguished there may be cures of cancer, senility, and other evils, so that happiness may outweigh unhappiness in the case of more and more individuals. Perhaps our far superior descendants of a million years hence (if they exist) will be possessed of a felicity unimaginable to us.

I regard Peter as one of the great moralists, because I suspect that more than anyone he has helped to change the attitudes of very many people to the sufferings of animals. Peter is a utilitarian in normative ethics, and a humane attitude to animals is a natural corollary of utilitarianism. Utilitarian concern for animals goes back to Bentham, who, presumably alluding to the Kantians, said that the question was not whether animals can reason, but whether they can suffer.

The reason why there are hardly ever completely knock-down arguments, except between very like minded philosophers, is that philosophers, unlike chemists or geologists, are licensed to question everything, including methodology.