Correct me if I'm wrong, but I believe you need to have actus reus (guilty act) and mens rea (guilty mind) to prosecute. Therefore, in addition to intent, the prosecution would have to show that throwing bubble gum on the sidewalk was an act that could lead to murder / lead to accessing a computer system without authorization. In that case, all this talk about what is/isn't authorized access still complies with the basics of common law because it defines what is an actus reus.

Disclaimer: IANAL either.