The reason why there are hardly ever completely knock-down arguments, except between very like minded philosophers, is that philosophers, unlike chem… - J. J. C. Smart

The sentiment to which [the utilitarian] appeals is generalized benevolence, that is, the disposition to seek happiness, or...good consequences, for all mankind, or perhaps for all sentient beings.

Men were made for higher things, one can’t help wanting to say, even though one knows that men weren’t made for anything, but are the product of natural selection.

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.