If we don't discount the future, we run into mathematical difficulties. The first rule of utilitarianism ought to be KIFS - Keep It Finite, Stupid.

Too much discounting runs into problems with screwing the future up, to enjoy short-term benefits. With 5-year political horizons, that problem seems far more immediate and pressing than the problems posed by discounting too little. From the point of view of those fighting the evils that too much temporal discounting represents, arguments about mathematical infinity seem ridiculous and useless. Since such arguments are so feeble, why even bother mentioning them?