I think there is some confusion here when going to class if you are sick is put in the same ballpark as a serial killer!
There are two sorts of 'right and wrong.' The first, which Helix is talking about in his sick/go to class example is very much a personal thing -- unless, of course, he considers contaminating others so they become sick, then he might want to stay in bed and have the material brought to him by a classmate! I assume you all still take notes?
But the matter of killing another human being is something else entirely, and has to do with a much more exalted (if you will permit the term) form of right and wrong which IS synonymous with good and evil.
While the concept of right and wrong is hardwired into us, the choice in the first example (sick/class) is not. This is not the case in the second example of killing. The killer knows it is wrong, even evil, and does it anyway. This is the person with the heart so hardened by sin and rebellion that life itself (except, possibly, for his own), means nothing to him.