I work at a hospital..what if one of our critical care systems were to be infected? Now, we have backups and take pains to ensure that no outside things can get in, but nothing is foolproof. If it affects the care of patient (I.e doctor cant get into a system to see past history of medications right away), who's fault is it?
What if it infects the police computer system, and a cop in a squad car cant identify a criminal who has a warrant out, and then he goes and commits murder that would have been prevented?
Extreme and unlikely examples, yes, but people who write such things open up the possibilities that this may happen and they should be punished.
Do they deserve the death penalty? I don't think so, but life is a reasonable sentence considering the systems that it could affect.