Even though I take a utilitarian view myself, I have a problem with utilitarianism, even of "rule utilitarianism," - at some point, utilitarians, who believe that moral actions are those that tend to maximize x )(happiness, fulfillment of desires, etc), will be asked to justify the utilitarianism itself. ("Why should we want to maximize x rather than y or z?") At that point, the utilitarian will either (a) have to justify their utilitarianism with some moral argument not itself utilitarian; (b) justify their utilitarianism with utililtarian reasoning; or (c) suggest that utilitarianism cannot justify maximizing x over y or z. (a) and (c) would render utilitarianism too flimsy by admitting that utilltarianism itself is not sufficient to account for all of the moral universe (which is important because once this is acknowledged, we have to question whether "the good" can be defined as "that which maximizes x" as there must now exist something "good (x) which does not derive its goodness from "its ability to maximize x." (b) would make utilitarianism troublingly circular, as justifying x by suggesting that "it effectively maximizes x" does nothing to answer the question "why justify x."
As I feel like the preceeding chapter contained too much philosophical jibberish, let me illustrate the point by rehashing a recent discussion on the atheist ethicist blog.
Its author, Alonzo Fyfe, is an advocate of desire utilitarianism, where moral action is defined as "that action which tends to fulfill desires." In his words, " A good desire is desire that tends to fulfill other desires." Conversely, a desire is not good when it tends to thwart other desires.
The desire utilitarian does not measure utility exclusively in terms of pleasure, happiness, well being, or preference satisfaction. Desire utilitarians say that the good is found in all of the things that we desire. It is found in happiness to the degree that we desire happiness, and it is found in pleasure to the degree that we desire pleasure. It is found in the company of family to the degree that we desire the company of family. All value exists in the form of desire fulfillment.
Aside from some problems I have with this style of utilitarianism (it is impossibly vague, malleable, and, at root, way more subjective and psychologistic than it aspires to be), it is question begging (as all forms of utilitarianism are). "Why is fulfilling desires considered "good"?"
Desire utilitarians could go for strategy (a), (b) or (c) above.
(a) "Fulfilling desires is "good" because fulfilling desires is what makes people happy and what makes people happy is good."
This is no good, because it tacitly admits that "good" is not defined by "ability to fulfill other desires. Therefore, it negates the desire utilitarians' claims "good" is defined in utilitarian terms.
(b) Fulfilling desires is "good" because fulfilling desires leads to fulfilling desires, which is "good."
While this option is the only one that stays "in bounds" of desire utilitarianism, the above answer is nonsensical because it is whoppingly circular. Further, it does not answer the question of why fulfilling desires is good (but only pushes the problem back a step.)
(c) Utilitarianism lacks the abillity to justify fulfilling desire (over some other variable) as the ultimate good on its own terms.
This seems to me the most honest answer. Utilitarianism always suggests that "good" is synonymous with "that which maximizes x" but cannot justify this as an ultimate valule on utilitarian grounds without being meaninglessly circular.
So why would I consider myself a rule utilitarian? I think that that moral actions are those which, if everyone acted the same way, would maximize liberty to pursuse their own happiness (within non-coercive bounds). But how can I justify my desire to see liberty to pursue happiness maximized?
I certainly cannot do it on utilitarian grounds (as liberty does nothing to maximize others' liberty). Like liberal pluralist William Galston, I throw up my hands and suggest that liberty is to be valued as a good simply becuase, if I had to guess, I would suppose that most people value liberty and would want to avoid coercion as much as possible.
Put differently, I am a rule utilitarian because I think that the best way to explain the morality of not stealing from others, helping others, and obeying traffic laws is that, the more people who do these things, the more liberty we and others will get to enjoy. While we sometimes have to do things (follow traffic laws, refrain from killing our bosses), the best reason to do these things - what makse them "good" - is that living in a world where there are traffic laws and rules against murdering bosses is more conducive to liberty than ones that are not.
Still, utilitarianism's fundamental flaw is that it, by itself, will always be incapable of justifying its particlar vision of what to maximize ("the good is what maximises fulfillment of desires,"). It will always have to resort to some extra-utilitarian justification somewhere along the way, lest it become viciously circular.