There are a number of arguments against utilitarianism; many of these take issue with utilitarianism's seeming lack of concern with the principles of justice, promises and personal loyalty. Other criticisms focus on utilitarianism's apparent impracticality. Still, some detractors take issue with utilitarianism's tendency to lead one to distasteful moral decisions.
One common argument against utilitarianism is that it does not assign inherent moral significance of justice. Utilitarianism is concerned with producing the greatest amount of happiness for the greatest number of persons. There are situations when just actions contribute to optimum happiness. However, it is also conceivable that in certain situations, a person or group of people are happier by doing that which is unjust. In such a case, utilitarianism seems to favor happiness over justice.
Another common argument against utilitarianism is that it is seemingly impractical as a governing philosophy for the general body of mankind. This is because utilitarianism is chiefly concerned with happiness, or pleasure. The problem is that human beings are extremely variable; individuals have their own conceptions of the pleasurable. Thus, creating a universal way of measuring happiness is problematic.
One of the biggest issues detractors have with utilitarianism is its basic premise that pleasure and utility are the determinants of worth. In Classical philosophy, things like virtue, knowledge, wisdom and temperance are good in and of themselves. In utilitarianism, they are only good if they have a demonstrable utility; otherwise, they may be discarded.