It can be argued that the utilitarian cannot consistently maintain that we should “hit the switch” and that it is wrong to save the five because both situations are virtually the same thing. In both situations, you are sacrificing one life for five lives. The total aggregate happiness would be greater for saving five people rather than one, therefore the utilitarian should agree to hit the switch and to save the five people. It doesn’t morally matter how the one person got to death, it’s just the fact that through utilitarianism you have to maximize happiness to the utmost extent and in both situations saving the five people would maximize happiness.
The Utilitarian can however argue that killing the patient would be wrong. In the train situation, the five people and the one person are already both on death’s door, which one of the two going to die. Therefore it is right to save the five people. However in the surgery situation, the five people are already going to die and the one person is perfectly healthy. That one person is going to live because of his health, so it’s not a matter of choosing who to die: the one person or the five people. It is a matter of murdering a healthy person versus letting five peopl die who are already going to die.