This is the primary problem with trying to pass a law in the wake of a highly emotionally charged event.
The people having the conversation regarding "common sense" concepts don't fully understand the concepts. Watch Mayor Bloomberg try to explain why supports a ban on semi automatic rifles by describing how an automatic weapon works.
He is either totally ignorant of that which he discusses or is being totally disingenuous in order to get his real agenda passed. Either way this is not the kind of people you want making new laws.
When making laws, you have to be VERY specific about the language and definitions. That opens the opportunity to take advantage of other peoples ignorance.