A prescriptively universalizing (and therefore utilitarian) critical thinker would encourage the adoption and development of firm principles and dispositions of the ordinary moral sort, rather than the direct use of utilitarian calculation as a practical working morality. There are at least six reasons why this is so. Shortage of time and energy will in general preclude such calculations. Even if time and energy are available, the relevant information commonly is not. An agent’s judgment on particular issues is liable to be distorted by his own interests and special affections. Even if he were intellectually able to determine the right choice, weakness of will would be likely to impair his putting of it into effect. Even decisions that are right in themselves and actions based on them are liable to be misused as precedents, so that they will encourage and seem to legitimate wrong actions that are superficially similar to them. And, human nature being what it is, a practical working morality must not be too demanding: it is worse than useless to set standards so high that there is no real chance that actions will even approximate to them. Considerations of these sorts entail that a reasonable utilitarian critical thinker would recommend the adoption of fairly strict principles and the development of fairly firm dispositions in favor of honesty, veracity, agreement-keeping, justice, fairness, respect for various rights of individuals, gratitude to benefactors, special concern for some individuals connected in certain ways with the agent, and so on, as being more likely in general to produce behavior approximating to that which would be required by the utilitarian ideal than any other humanly viable working morality.
Mackie, J. L. (1984) ‘Rights, utility, and universalization’, in R. G. Frey (ed.) Utility and Rights, Minneapolis, pp. 91