A calculus of comparative consequences is impossible. Every effort to develop one is a process of rationalizing bias.
Consequentialism assumes, based on experience or thought experiments, that it can assess the consequences of a particular act. This position implies that one act causes consequences. These consequences can be evaluated, reduced to some kind of common metric, and then compared to other actions and their consequence to determine which action is best.
At the most broad philosophical level, consequentialism raises the problem of causality and induction. The problem of causality is one can never be certain that one event causes another. The problem of induction comes up when one makes assertions about circumstances where one has no experience by assuming that they are similar to circumstances where one does have experience, e.g., actual events are similar to counter-factual ones.
Therein lies sufficient grounds to reject consequentialism. One can never be certain consequences were caused by a particular act. Further, even if one wanted to pretend that one can draw a line between an act and a consequence, there is no way to be certain one is accounting for all relevant consequences.
Suppose it is possible that one can draw a line between an act and a consequence and that all morally relevant consequences can be accounted for. Consequentialism also claims that it can compare among the many different possible outcomes and determine which is “best” according to some criteria.
This assumes two things. One, it assumes that not only can one account for all relevant consequences in circumstances that actually occurred, but one can also do so in evaluating the consequences of actions that were not taken. This is the problem of induction, where one assumes that some possible course of action would happen with consequences similar to what one has experienced in the past.
Consequentialists defend against the problem of induction by saying that consequentialism is not intended as a guide for decision making but as a standard for evaluating consequences after the fact. Yet, the standard still requires making comparative judgments about acts that did not happen, which is as impossible to know as knowing all consequences in advance before acting. Making this distinction does not help them.
Pretend for a moment that even if one’s sense of consequences is not perfect, it is enough to draw useful moral distinctions. Now, suppose one has a billion US dollars, and one decides to invest it developing a space elevator. Based on consequentialist moral standards, which out of the infinite number of ways or combination of ways one could have spent that money is best? For example, it could have been used to provide clean water and food to people starving or suffering from food insecurity, eliminate disease through vaccination programs, train physicians, etc. Ultimately, any assertion of which way is best is based on a value judgment that comes before the consequences. If one thinks eliminating suffering right now is more important, then one is going to think an action aimed at addressing the here and now, such as alleviating hunger, is preferable to a space elevator even if, in the long run, the space elevator may have better consequences.
Consider the Trolley problem, where a trolley is out of control and going to kill five people and you only have the option to throw a switch which will turn the trolley down a track to kill one person. What is the “best” outcome? Aside from moral questions about the responsibilities of the actor and committing harm, how does one value the lives in this and other hypothetical scenarios? If these five people being saved are a criminal gang, then it seems difficult to argue that saving them would result in the most happiness for everyone. Or, perhaps the person being sacrificed is a once in a generation talent of some kind and the other five bring less happiness than this gifted person on one’s consequential scale. On the other hand, perhaps the criminal gang will eventually turn into good people that bring better net consequences than the person that was sacrificed. The only thing that is certain is that all lives do not have equal consequences, and it is impossible to tell what they are if some of those consequences remain in the future, and every action of current moral import will have future implications.
So, what is consequentialism really doing when it says it is evaluating consequences, when in fact it cannot? It is cherry picking moral options and which consequences are relevant. If one dictates the premises, one can dictate the conclusion. It’s a system for rationalizing bias. At base, consequentialism is a morality market with only one buyer determining the value (consequences) of different products (actions). And, like any market, there are externalities that are not factored into the price that are borne by society at large or are simply ignored. It’s a terrible basis for a morality.