Explain, and critically assess, Bentham's (Classical) Utilitarianism

(Introduction)
Jeremy Bentham's Classical Utilitarianism is an ethical doctrine founded on the principle of utility - that that which promotes the most happiness or pleasure is the (morally) best action, and that which causes the most amount of pain is what ought to be considered the least morally favourable course of action, or indeed an altogether immoral action. However, despite how intuitive utilitarianism appears, given that we are all capable of being intentionally and unintentionally hedonic in our every day behaviour, it has several fundamental flaws. In the course of this discussion, I shall firstly explore how utilitarianism is a perspective that necessarily favours moral realism - a theory claiming that there are absolute facts about morality in the world - and how this position leaves utilitarianism open to attack from moral sceptics and relativists. I shall then explore that, if moral realism were true, then it isn't necessarily the case that the notions of pleasure and/or happiness are what determine moral facts in the world, for they may in themselves not constitute moral truths. From this I will develop a discussion into utilitarianism's internal issue: that the moral subjectivity of individuals causes an internal relativistic conflict. For example, if half of a room are torturers, and the rest their victims who fear pain, how, if at all, can it be clear what is morally right in the situation? My concluding argument, to make an appeal to Nozick's 'Experience Machine', will then criticise utilitarian doctrine on the grounds that it is conceivable that there is something about the nature of experience and reality that forces us to reconsider how pleasure and happiness are to be valued, given that reality is conceivably better than simulated, eternal pleasure.