Evaluate Bentham's act utilitarianism.

Bentham's act utilitarianism is a consequentialist, hedonistic ethical theory, which seeks to provide a means of determining which course of action is the most moral one available to an agent in a given situation. From the principle of utility, which states that a moral action is one which promotes the greatest good for the greatest number of moral patients, under Bentham's system the agent must use the hedonic calculus to determine whether an action achieves this end, from criteria such as the fecundity, duration, intensity, etc... of pleasure that would be brought about by it. It can be seen from this that Bentham's act utilitarianism possesses a key strength over deontological theories based on large numbers of maxims/axioms in that it seeks to be more generally applicable, using its one maxim of the principle of utility as its axiomatic base to prescribe courses of action in a multitude of scenarios, rather than to provide many different maxims for various situations (as is the case with Kantian ethics' 'do not lie', 'do not commit abortion', etc.). However, the fact that act utilitarianism takes pleasure (as a basic experience of all sentient beings) as the basis of all of Bentham's subsequent ethical theorising leads to significant problems for the theory of a whole, and at worst shows his system to be fundamentally flawed. Bentham takes as his starting point a phenomenon which is common to all beings capable of being moral agents and moral patients (typically humans, although this potentially extends to animals with higher states of cognitive functioning) - the ability to experience pain and pleasure. He maintains that the key question that should be asked in the formulation of an ethical theory should be 'can these agents think?', but instead 'can they suffer?'. This is all well and good, as undoubtedly if one makes or experiences the results of an ethical decision they will undoubtedly feel some degree of pain or pleasure. But Bentham then makes an unjustified leap from the descriptive observation that 'sentient beings can both suffer and experience pleasure' to the normative claim that 'it is wrong for sentient beings to suffer'. He never explains explicitly as a step in his argument exactly why the mere fact that beings can suffer makes it wrong that they should, and thus commits the naturalistic fallacy in moving from a descriptive to a normative claim without further justification. Therefore, we can see that because the naturalistic fallacy lies at the heart of the thinking which prompts Bentham to propose act utilitarianism as an ethical theory in the first place, without this further step in argumentation his whole theory risks being invalidated through an insecure theoretical basis. Furthermore...