In utilitarianism, it is viewed as morally correct to do what will create the most benefit across the most people. Slavery would be an example of something that is morally wrong, as it hurts the slaves more than it benefits the master. In this manner, we can arrive at nearly any reasonable moral conclusion. Also, it is unfeasible to try to reconcile this with deontological thinking as that would mean that certain things are ALWAYS right or wrong regardless of the consequences. It can be determined what is right in a utilitarian system by weighing values and people against each other justly. Utilitarianism did not justify slavery. Slavery, like abortion today, was justified with the argument that those they were doing it too were not really people, and that therefore the moral laws did not apply to them.
Utilitarianism is a theory in normative ethics holding that the best moral action is the one that maximizes utility. Utility is defined in various ways, but is usually related to the well-being of sentient entities. Originally, Jeremy Bentham, the founder of Utilitarianism, defined utility as the aggregate pleasure after deducting suffering of all involved in any action. John Stuart Mill expanded this concept of utility to include not only the quantity, but quality of pleasure, while focusing on rules, instead of individual moral actions. Others have rejected that pleasure has positive value and have advocated negative utilitarianism, which defines utility only in terms of suffering. As opposed to this hedonistic view, some define utility with relation to preference satisfaction whereas others believe that a range of values can be included in its definition.
Utilitarianism is a form of consequentialism, which states that the consequences of any action are the only standard of right and wrong. This view can be contrasted or combined with virtue ethics which holds virtue as a moral good. Some believe that one's intentions are also ethically important. Utilitarianism is distinctly different from other forms of consequentialism such as egoism as it considers all interests equally. Proponents of utilitarianism have been split about whether individual acts should conform to utility (act utilitarianism) or whether agents should conform to ethical rules (rule utilitarianism). Utilitarians additionally remain split about whether utility should be calculated as an aggregate (total utilitarianism) or an average (average utilitarianism).
Historically, hedonism can be traced back to Aristippus and Epicurus who viewed happiness as the only good. Bentham is, however, credited with founding utilitarianism when he wrote An Introduction to the Principles of Morals and Legislation. Since Bentham, prominent utilitarians have included John Stuart Mill, Henry Sidgwick, R.M. Hare and Peter Singer. The philosophy has been applied to modern issues including the suffering of non-human animals. Specifically, utilitarianism has been applied to the ethics of raising animals for food and the ethics of wild animal suffering. Effective altruism is a philosophy aimed at improving the world through evidence based means, which has been supported on utilitarian grounds.
Opponents of utilitarianism have criticized it for many reasons. Some have said that utilitarianism ignores justice while others contend that utilitarianism is impractical. Specific criticisms have included the mere addition paradox and the utility monster. Others have said that pleasure is not commensurable across people with varying identities and thus the idea of aggregating utility is impossible.
Utilitarianism by itself does not preach a behaviour. It does however shed light on the very strange and varied behaviours that humans demonstrate.
It is important to understand that the pursuit of pleasure or the avoidance of pain lies behind all of our actions or else we will be forever in conflict and befuddlement.
It is also important to understand that we do not view all pleasures as having the same value or we would never force ourselves to speak publicly or fight to defend something or endure hours of guitar practice. The goal or the pursuit of the goal itself provides pleasure that is sometimes difficult to describe but we feel it nonetheless.
Sometimes, people who appear to benefit from actions are hurt in ways they do not know. Slavery not only hurt the slaves it hurt the slaveowners. Anyone who has gotten pleasure from someone else's discomfort and then come to know that person and get pleasure from their friendship will almost always tell you that there was much more pleasure in the friendship. Slaveowners benefitted financially but their growth was stunted spiritually. Their daily blunting of their capacity to feel empathy robbed them of experiences that could have been truly wonderful.
Human beings are progressing only because we have come to recognize that there are powerful peaceful pleasures that come from actions that seem altruistic. There is no such thing as altruism. The pleasure that altruism type of behaviour brings to the doer, the observer, and the recipient has been well documented. Our failure as a society has been in getting this information out to everyone.
Utilitarianism gives us the tools to start to understand and proclaim why the seemingly high moral ground can be such a rush for anyone standing on it. This ground is even better when shared with others. The only sin is denying ourselves this pleasure.
Read more at Pleasureworks: Pleasure is the highest good
Utilitarianism is a meta-ethical system. It only states that the best action is the action that creates the most good.
Now, the definition of good can be debated (happiness, freedom, etc). But do not mistake Utilitarian Hedonism (a la John Stuart Mill) for Utilitarianism. After all, the 'good' can be whatever we define it to be, and utilitarianism is simply about achieving those ends in the most efficient way possible.
The utilitarian doctrine has its holes, sometimes it overlooks individual rights. Slavery for example: the economy of the South was greatly boosted at the cost of the liberty and dignity of the enslaved Africans. Morality is not defined by one ethical doctrine, all the various moral theories that philosophers developed play a role.