Because robots do not have emotions that will get in the way. As humans, our emotions play a huge part in our decision making. If you think about it, many of the decisions we make as humans are based on what we are feeling. We do certain things because we are feeling a certain way. Even though it isn't smart, someone might throw a punch based on anger. That means that robots always make the choice that will be the best because their choices are not emotionally motivated. They are also programmed to do so.
