Utilitarianism is generally defined as the principle which upholds in the world that the right course of action is the one which maximises the overall good or the good of the many over the good of the few. It is a pragmatic and quantitative approach to ethics reducing it merely to a mathematical standard of morality.

When they speak of things like maximising good to the maximum number of people, they fail to determine what ‘good' really means and on whose standard of good are we to take reference. Adolf Hitler thought it would be for the overall ‘good' of the human race if only White, blue-eyed, and blonde-haired people mated and reproduced and thus producing a homogenous humanity where there would be no conflicts, obviously, because all the other races have been wiped out by genocide. So it really all comes down to those laying down the rules of terms like happiness and good.

Utilitarianism being a primarily western philosophy (if you can call it such a thing) and could not apply to eastern countries because their value system is completely different to that of the west. Even within a country or a society, the definition of good and happy varies from epoch to epoch. Utilitarianism study human nature enough before it jumps to conclusions which is ironic considering that utilitarianism was formulated to better the overall condition of humanity.

Such a theory would not consider any non-human species either or if considered it would only be those which add to or are necessary for the life of the human race because the theory itself was conceived by humans. This would conflicting to the very foundation of utilitarianism because human beings are only one species on the planet and all other species (Flora and Fauna) put together are much larger in number. This would mean, from a purely utilitarian perspective, that for the greater good of the majority of the species, the human race would have to go extinct since it is us that have inflicted the most amount of damage on the rest of the planet since the industrial revolution.

Average utilitarianism argues that it would be ‘immoral' to add an averagely happy person to a group that is very happy. This would of course lead to a morbid and crude conclusion that less happy people should be isolated or even eliminated from the rest of the world who are supposedly happy. This would defeat the very purpose of utilitarianism as majority of the people in the world are not happy or are unsure about their psychological state. One cannot split the human condition into two states of happy and unhappy without defining what happiness really is. Defining happiness, again, would be an impossible and impracticable task as everyone has a different value system and different things make different people happy. Therefore, it is almost impossible to make everyone happy without one's happiness conflicting with the happiness of others. Seclusion of less happy people would only weigh on the guilt of the so-called happy people as well. This is especially true with concepts like Total utilitarianism which states that it is good to breed more people as long as total happiness rises.