1. Other people may argue that the trolley case and surgeon case are the same. When you choose to save the 5, you choose to kill the one at the same time. Utilitarian think it would be wrong to save the 5 in the surgeon case violate their ultimate goal that maximum happiness.
2. Utilitarian may argued that in the trolley case, the ultimate goal for utilitarian is to maximum happiness, therefore, they think we ought to hit the switch to save 5 lives to reach maximum happiness. However, in the surgeon case, when you save those 5 people. You also make a choice for a healthy person. But we do not have the right to make choices for other people. Also, maybe letting those 5 people die is a release for them. It could achieve more happiness than saving them.