Ethics: A Pluralistic Approach to Moral Theory (2nd ed.), pp. 179-202, and Mr. Hinman’s website at http://ethics.acusd.edu)
Philosophical Utilitarianism comes in two basic "flavors": Act-based Utilitarianism and Rule-based Utilitarianism.
In Act-based Utilitarianism we examine an individual act and attempt to figure out the utility each time the act is performed.
Rule-based Utilitarianism is more categorical in nature. In a way that makes us think of Kant a bit, it looks at the consequences for having everyone follow a rule. We then try to calculate the overall utility of accepting or rejecting the rule.
I am going to modify an example given by Mr. Hinman to illustrate the difference between the two schools of thought: Dr. Jones, a highly respected Nobel Prize-winning medical researcher, announces that he has discovered a way to cure AIDS. However, on the way to the meeting where the formal announcement of his discovery will take place, he has a serious car accident that leaves him in critical condition. He needs a heart-lung transplant immediately in order to survive, but no suitable donors are available. However, in the indigent clinic is an unconscious man with no family who is being kept alive on a respirator, and who will almost certainly die in a few days anyway. Should the transplant team "borrow" the organs of the dying man to save the researcher, whose discovery could benefit millions?
Rule Utilitarians would probably say "no"—at least at present, our society would not permit a general rule allowing the harvesting of organs from unconscious people, homeless or not, especially without their consent. It would be both a breach of public trust, and also undermine public trust in the medical establishment.
Act Utilitarians might find a find a different answer, especially if secrecy could be guaranteed. The hastened death of one person would be a small price to pay compared to the good of saving the AIDS researcher.
Rule Utilitarians claim that Act Utilitarianism is too quick to justify the breaking of moral rules and the violation of individual rights. Doing everything on a case-by-case basis also takes too long.
Act Utilitarians reply that following rules that violate overall utility is foolish rule-worship. Rules can be violated when consequences demand it. Also, such extreme cases are probably fairly rare; most questions can be solved by following rules, moral codes, and "rules of thumb," or "accumulated wisdom based on past consequences."
Both types of Utilitarianism may run afoul of the problem of who does the moral calculation of deciding what is best. Example: The American government would like to provide economically deprived persons with the means to improve their situation in life. However, well-intended solutions offered by well-meaning bureaucrats and social workers may be repulsive or even do harm to the people they are trying to help.
There is also the "Who exactly are we helping at whose expense" question. Our group? Our nation? Our race? Our future generations? Our species? How do we count pain or suffering of animals in our moral calculations?
Mr. Hinman concludes: "Utilitarianism is most appropriate for policy decisions, as long as strong notion of fundamental human rights guarantees that it will not violate rights of small minorities."