Have a look at the Strengths and Weaknesses of Utilitarianism.
Bentham - The Hedonic Calculus
There are some circumstances when you can usefully use the calculus as a guide to determining the overall effects of a course of action, such as in choosing how to spend lottery money, or in deciding how to prioritise medical procedures in a hospital. However, many of our moral decisions do not have predictable or measurable outcomes at all. It is unclear what counts as pleasure or how to equate pleasure and pain. There are three key points here:
- Unpredictable - You can't know the future, and things rarely turn out as we think they will. It cannot be right to judge an action right or wrong based on outcomes that are down to chance.
- Incalculable - Even if you knew exactly what would happen, it is impossible to add up all of the pain and pleasure resulting from a course of action. There's simply too much to calculate
- Immeasurable - A more fundamental flaw. Even with the simplest event - choosing whether to buy a toy or a magazine for a child - it is impossible to decide on a value to give for happiness. Is the joy of reading a magazine more intense than the joy of playing with a toy? Pleasure cannot be measured, so the idea of adding it all up doesn't work.
There is also something instinctively wrong with judging the morality of an action by it’s outcome – a person motivated solely by greed or revenge might choose a course of action that happens to make the greatest number of people happy. Does this make him a good person? Even more concerning is the possibility of sadists whose pleasure at torturing others is so great that this in itself makes their actions good. The theory seems to support the exploitation and abuse of minority groups if it pleases the ruling majority.
Mill - Higher Pleasures
How do you decide whether white-water rafting is a higher-level pleasure than listening to Beethoven played live or eating an Indian takeaway? Mills theory seeks to reduce everything to a consideration of happiness, when moral decisions are actually a lot more complicated than that. It also still allows for great injustices to be carried out just as long as the greatest good is served.