Why should one adopt utilitarianism rather than some other moral philosophy? This essay explains four simple principles from which the utilitarian position follows.
First, the purpose of morality is to do what is good and prevent what is bad. I hope no one disagrees with this.
Second, I define good in relation to myself by my interests or preferences. The things that I value for myself–physical health, intellectual engagement, human connection–I consider to be good for me. The things I want to avoid, I consider bad.
Third, all beings who hold interests deserve moral consideration. While I cannot experience anything beyond my own consciousness, I still must recognize the existence of consciousness outside of myself. Even though I cannot directly experience the good that others feel, I must acknowledge that good exists for others just as much as it does for myself. I hold certain interests and other sentient beings hold their own interests; I ought to respect their interests just as much as I respect my own . I want to do the most good possible–even if the good affects others and not myself.
Fourth, an interest holds value in proportion to the strength of the interest. My desire for life overrides my desire for an adrenaline rush, so I do not jump off of a cliff. Similarly, different beings’ interests may be compared by considering the strengths of their interests.
Those who do not accept this claim have no way of judging one particular good as more significant than another. However, I cannot deny that some of my interests are more important than others, and it is worth violating a lesser interest to serve a greater one (e.g. giving up my temporary happiness by cleaning the dishes so that I can use them later). From this fact, it follows that some people have some interests that outweigh other people’s interests. For this reason, tyranny of the majority is unjustifiable, as the minority’s stronger preferences outweigh the majority’s weaker preferences. (For a more detailed explanation of why it is possible to judge one good as more significant than another, see “Measuring Happiness.”)
This is not to say it is always easy to determine which interests matter most. Doing so is often difficult, but rarely (if ever) impossible.
Utilitarianism is simply the combination of these four simple premises. Good is defined by individuals’ preferences; all beings capable of having preferences deserve moral consideration; some preferences take precedence over others. From these principles, one may determine (or at least approximate) the most ethical choice in every situation.
 Here, "respect" simply means an acknowledgement that the interest holds value. Some interests promote the general good more than others; for example, a desire to provide for one's family does more good than a desire to indiscriminately murder people. If someone wanted to commit murder, I would try to prevent him from doing so, but only because the potential victim's desire to live overrides the potential murderer's desire to kill, and not because his interests do not hold value.