Utility and such

My understanding of Utilitarianism is thus: That a decision is moral if the outcome of that decision creates a greater amount of good than it does evil. This can be applied to small as well as large scale situations. What I am still a bit confused about is too whether or not Mill believes that this is something that rational people will just naturally do, or if it is the course of action we should, rather than always do, take. For example, if we always put the idea of the "Greater Happiness" theory to work, everyone would a vegan. Mill, and most contemporary Utilitarians I know of, were animal rights activists.

To Mill, it matters very little whether from an epistemological standpoint a person is an emphirist or a rationalist, believes in a priori principles or learning through experience. The fact of the matter is, according Mill, is that ALL ethical theories have one thing in common - the ultimate goal is happiness. Thus, he doesn't feel that he needs to provide a much further proof, than that all other theories revolve around the notion of happiness. He has simply forged from that a more comprehensive, sensible, from his perspective, theory. He believes that certain things are simply desirable - if one desires money, he will work within the context of the socio-economic structure to earn that money. Likewise, if one desires to create happiness, he will work within the context of an ethical system (Utilitarianism) that creates the most happiness.