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 t… - J. J. C. Smart

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.

Normally the utilitarian is able to assume that the remote effects of his actions tend rapidly to zero...It seems plausible that the long-term probable benefits and costs of his alternative actions are likely to be negligible or cancel one another out.
An obviously important case in which, if he were a utilitarian, a person would have to consider effects into the far future, perhaps millions of years, would be that of a statesman who was contemplating engaging in nuclear warfare, if there were some probability, even a small one, that this war might end in the destruction of the entire human race. (Even a war less drastic than this might have important consequences into the fairly far future, say hundreds of years.) Similar long term catastrophic consequences must be envisaged in planning flight to other planets, if there is any probability, even quite a small one, that these planets possess viruses or bacteria, to which terrestrial organisms would have no immunity.