Utilitarianism
PRINCIPLE OF UTILITY
Utility was defined by Bentham as “the principle which approves or disapproves of every action whatsoever according to the tendency which it appears to have to augment or diminish the happiness of the party whose interest is in question.” The principle of utility is designed to promote the happiness of the individual or the community. The community can have no interests independent of or aggressive to the interests of the individual.

Bentham's theory of utilitarianism asserts that actions and institutions should be judged by their contribution to utility, which is measured by calculating the relative contribution to happiness or pleasure, as opposed to pain.
It has been pointed out that not only is pleasure difficult to measure, but that utilitarianism provides neither any guarantee of individual rights against majority interests, nor any means of weighing high levels of pleasure for a few against lower levels of pleasure for greater numbers.

http://www.utilitarian.org/faq.html
What is the utilitarian position on monogamy vs. polygamy, marriage and adultery, capitalism vs. socialism, the legalisation of cannabis etc?
It is a common mistake to suppose that utilitarians have a fixed approach to controversial political issues. While utilitarians agree on what the criteria for good social policy are (being its conformability to utility), we freely and commonly disagree on which policies are actually useful. We know which goals we should aim for, but we are no better equipped than any others in politics to decide which policies will, in practice, help us achieve those goals. One may ask a utilitarian what makes people happy, but one would be unlikely to receive a better answer than can be given by the psychologist. One may ask a utilitarian about the national debt, but would be unlikely to receive a better answer than