To begin with, recall that utilitarianism is the name given to any ethical theory that says something is good if, overall, it brings about utility (in other words, well-being or happiness). This is referred to as the utility principle.
There are many potential advantages of utilitarianism. Firstly, it is especially well equipped to avoid bias in ethical evaluation. If you consistently apply the utility principle, then you won't privilege your own minimal enjoyment over the greater benefit that someone else could receive.
The calculation of consequences also brings utilitarianism close to the scientific investigation into things. Both make observation and prediction central to their practice.
But there are many disadvantages too. One problem of basing ethics in calculating consequences is that we can’t predict all the potential outcomes of human actions in the same way that we can predict the effects of physical things.
But if you can’t know whether the consequences of your action will ultimately be good or bad, then it seems that you can’t guide your action with the utility principle.
It’s a lot to ask someone to try to calculate all consequences. Plus, the burden of weighing up all consequences can mean that you have to take other people’s happiness as seriously as your own. This is a tall order for our daily lives. Moreover, utilitarianism makes us responsible for the things we don’t do as much as the things we actually do.
As we have seen, utilitarianism provides ethical evaluations that sometimes make sense to us, but sometimes don’t. In other words, it can give us both intuitive and counterintuitive results.
One of the reasons utilitarianism is sometimes intuitive is that it appeals to our sense that the effect of our actions on other people matters.
Imagine you’re driving around trying to find a parking spot. You come across three spaces together, but you’re feeling too lazy to park properly in one spot. You park sloppily, taking up all three spaces.
Most people would think this is completely unjustified. The utilitarian would agree, arguing that the utility for three people to park their car outweighs your convenience.
One of the reasons utilitarianism is sometimes counterintuitive is that the emphasis on consequences means intentions are left out of the picture. If someone has bad intentions, but accidentally brings about utility, then the utilitarian will have to say they are good. This doesn’t make much sense to most of us.
We may be grateful for the accidental result, but we don’t want to say the serial killer’s action itself was good.