Learning about ethics and moral reasoning is important for many different reasons.
First, for some people, doing the right thing is important on a personal level. I would say most people are like this. Who would feel good about doing something immoral? The conscience is a powerful motivator in ethics.
Second, many people believe that ethics are very important for society to function well. Without ethics, society would break down. Therefore, it is important for people agree upon a set ethical outlook.
Third, there is also a religious reason for many people. Ethics are central to many religions. One only needs to think about the Ten Commandments from a Jewish or Christian perspective.