For example, many individuals value freedom and knowledge as things that can bring happiness. So, having their own value, these things are parts of happiness.
Mill believed that everyone's happiness is important. He believed in what he called the 'greatest happiness principle.' According to the greatest happiness principle, a person is ethically required to try to bring about the consequences that would lead to the greatest amount of happiness for everyone affected. More simple stated, if a person can produce more happiness (and/or less suffering) in a certain situation, then he or she is ethically obligated to do so. In more contemporary ethical terms, this is called the requirement to 'maximize happiness. If one was considering doing something for one's own happiness, but that action would cause others suffering, then Mill would have to take both of the sides into account in deciding whether or not the action should morally be taken. For the utilitarian, every single individual's happiness must be considered. This is what Mill called the 'equal consideration of interests.' Under this way of thinking, everyone counts for one and none for more than one -- that is, one's happiness or suffering cannot be weighed more or less than anyone else's when it comes to deciding an action to take. This goes for everybody, whether the person is someone in the family or a complete and total stranger.
Mill's utilitarian moral theories also examine the moral worth of action on the basis of happiness that is produced by an action. Whatever action creates the most happiness in the most people is the moral course of action. Kant objected to utilitarian theories, believing that they devalue individuals that the theories are supposed to benefit. If one is to follow his or her utilitarian calculations to motivate his or her actions, he or she is allowing the valuation of one individual's welfare and interests in terms of what good they can be used for. Under utilitarian theories then, it would be possible to justify the sacrificing of one person for the benefit of other people if the utilitarian calculations promise more benefit. Doing this would the treating an individual completely as a means and not as an end in themselves.
According to Mill, just the feeling of happiness can teach every human to be tolerant of each other and develop the inner desire to be in unity with other humans. This feeling is what helps individuals care for others, worry about others, and to not have individual interests and to not follow selfish goals, but rather, see interests that are associated with others. There is some skepticism for many here because it does not seem possible that one can always act with general happiness as a main goal. However, Mill would find progress where people begin to take others' happiness -- even stranger's happiness -- into consideration and have it become an important factor when making a decision about what to do. This is the greatest stage of morality for Mill and he strongly believed that society must move in that direction (Mill 2010).
Both Kant and Mill have very interesting theories on happiness, however, both definitely have their own limitations. While Kant believes that happiness and morality is solely based on reason, motivation is not always based on rationalism, but rather, it is more likely based on one's desire to be happy. Desiring happiness does not seem like something is purely rational at all; happiness, rather, is something that is more primitive -- it is more of an emotional and unconscious feeling; it is something that is ingrained into all humans without them even being aware of it. Mill's theories on general happiness is an easier concept, obviously arguably, to accept. It seems easier to accept the notion that each individual has their own interests and goals and ideas about what will bring him or her happiness, but there is also an idea about the greater happiness of mankind. There are things like freedom, knowledge, peace, and security that are incredibly important to people -- and these are examples of general happiness. Those values are just as valid as anything else in this world and they are what make up moral principle; these can be applied to the greater society.
Kant, Immanuel. (2009). Fundamental principles of the metaphysic of morals. Merchant Books.
Mill, John Stuart. (2010). Utilitarianism. CreateSpace.