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. This is referred to as the utility principle.
One reason utilitarianism is an attractive ethical theory is that it fits with our common view that ethics should be about the group, not just the individual. That’s because calculating the overall utility of an action or rule must include the consequences on other people as much as ourselves.
The utilitarian backs this up. If a library book is damaged, the utility it can have has been drastically reduced since no more people can get pleasure out of it.
Utilitarianism shows a concern for other people, in future times, as well. In other words, it gives us ethical reasons to care about the generations that follow from us, and the fate of humanity more generally. That’s because the consequences of our actions can greatly affect the future.
You can extend this idea to think about the environment more generally. If our actions damage the conditions of human life (e.g. clean air, water, etc.), a utilitarian would say it’s wrong.
Since utilitarianism says the goodness of something comes down to its consequences, it needs to be fairly good at predicting consequences if it wants to guide action. It does this by looking at as much information as possible; not just whatever is at hand.
For this reason, utilitarianism has some similarities to science. As you know, science puts a lot of emphasis on observation for providing explanations or predictions of how things work. Although you can’t be as accurate at predicting the effects of human action as you can when predicting how physical things work, they’re still both informed by empirical research. Many people are attracted to utilitarianism because of this fact.
You might also think utilitarianism has something going for it because we use its methods in other areas of our lives. For instance, we make some laws based on how much utility they give us.
There are many other examples like this. For instance, there are laws in place to make sure that divorces are fair to both parties. The laws here aim to have the greatest utility.
Despite the similarity between utilitarianism and civil law, you should be careful not to confuse them. Utilitarianism isn’t meant to be a legal system. It just so happens that legal systems often use similar tools as does this particular ethical system.