Good and bad are both relative subjects, and what one person does may or may not be considered bad to another. This is dependent on context because what on person does may be justifiable to them and their intended outcomes, but from the perspective of another party may be seen as bad. For instance, would Robin Hood be considered bad for stealing or good for giving to the poor?
The idea of bad people is not a myth. Not only are evil tyrants and dictators such as Hitler and Stalin, but murderers and rapist are bad people too. Sometimes it is not politically correct to say someone is a bad person, but it is important to do so at the right moments.
Making bad decisions is the result of being led down the wrong path. The wrong path is gone down when the person believes or is taught to do something in a way others Beleive is incorrect or wrong. A few decisions in one's life cannot direct that persons whole life.
Type "define bad" into Google. The first definition pulled up will read "of poor quality." To reiterate the question, "is the idea of a person HAVING POOR QUALITIES a myth?" Of course not. In fact, based off of this definition, everybody should be considered a "bad" person. We all possess poor qualities.
From our earliest ages we rebel against our parents, our teachers and other who have been placed in authority over us. This is evidence that we continue to do bad things, which must mean we are bad people. Again, not as bad as we could be, but definitely a little bad in everyone of us.
There are some people that are just bad. It can be argued that they may have been good once and corrupted by a twisted society, or some other excuse for the behavior. If that were really the case, all children in a similar situation would turn out to be just as bad. That is not the case. Some people just have an urge inside them to do bad things, and they listen to it often.
I believe there are some people on this planet that are just bad people. That's not to say that they are bad people in every facet of their life or that some people don't see them from a different perspective. I believe it would be difficult to argue that all people are good as well.
No, the idea of a bad person is not a myth, because we all have good things and bad things in us. People can be very good and show each other extreme amounts of love and compassion. On the other hand, people can be cruel, and can be extremely vicious to each other.