If Mill is going to obey his own theory he would say that only killing one person would be less harmful than killing all four of the people. If having one person die in contrast to having all five die a utilitarian would chose to kill one person and save four people. Mill’s decision would be solely based upon his own theory of promoting happiness to the greatest number of people.
Personally I do not agree with Mill’s theory. What is good for the majority is no necessarily good for the minority. Just because one is not in the majority group does not mean they do not have rights either. Always pleasing the greatest number of people is not always the right thing to do.
When a utilitarian if faced with a problem they have the right considerations but do not give a realistic way to gather the right information to make the right decision. There is not enough information in evaluating the welfare of an issue along with the consequences that may or may not go along with the decision.
There is no way to determine which people will be killed and weigh whether their deaths would be good for society. Utilitarianism requires that one compare the good that the people would do for society with the harm they would do society if they were not killed. The problem with this is that a person faced with making the decision cannot get the exact information. Even through experience, it is hard to judge how much of an outcome each action has on its decisions.
A Utilitarian looks at every problem the come across as an equation. In killing 5 people compared to 1 a utilitarian would think of it as 5>1, meaning that 5 people are greater than one so the greatest good would be to save the 4 people and have one die. The greatest good for the greatest number would be to have four people live opposed to having five people die.
Utilitarianism is a concept that has been around for a very long time.