Utilitarianism is a philosophical view or theory about how we should evaluate a wide range of things that involve choices that people face. Among the things that can be evaluated are actions, laws, policies, character traits, and moral codes. Utilitarianism is a form of consequentialism because it rests on the idea that it is the consequences or results of actions, laws, policies, etc. that determine whether they are good or bad, right or wrong. In general, whatever is being evaluated, we ought to choose the one that will produce the best overall results. In the language of utilitarians, we should choose the option that “maximizes utility,” i.e. that action or policy that produces the largest amount of good.
Utilitarianism appears to be a simple theory because it consists of only one evaluative principle: Do what produces the best consequences. In fact, however, the theory is complex because we cannot understand that single principle unless we know (at least) three things: a) what things are good and bad; b) whose good (i.e. which individuals or groups) we should aim to maximize; and c) whether actions, policies, etc. are made right or wrong by their actual consequences (the results that our actions actually produce) or by their foreseeable consequences (the results that we predict will occur based on the evidence that we have).
See here, me and utilitarianism would almost agree - it's fairly similar to my basis of groundwork, its the interpretation that I take issue with.
"To illustrate this method, suppose that you are buying ice cream for a party that ten people will attend. Your only flavor options are chocolate and vanilla, and some of the people attending like chocolate while others like vanilla. As a utilitarian, you should choose the flavor that will result in the most pleasure for the group as a whole. If seven like chocolate and three like vanilla and if all of them get the same amount of pleasure from the flavor they like, then you should choose chocolate. This will yield what Bentham, in a famous phrase, called “the greatest happiness for the greatest number.”"
Because it assumes the pleasure of ONE PERSON equals the pleasure of ONE OTHER PERSON, when that is not always the case, or actually almost ever.