"Good and bad," Where do we get these notions?
This is an interesting question and I am sure that you will get many different responses. In my opinion, one of the best way to look at this question is by looking at it from the perspective of sociology or cultural anthropology.
These two disciplines state that each society has its own way at looking at things. In other words, each society has its own commonsense view of the world or a cultural idiom of what is right and wrong. For this reason, we can say that each society has its own notions of "good" and "bad." These categories are culturally conditioned to a certain extent. Thinking about categories of thought from a cultural and sociological perspective will give you a lot of intellectual mileage.