If any lawyers want to contribute to this, please do. In my post Shodan: Another Step Towards Intrusion as a Service, some comments claim "negligence" as a reason why intruders aren't really to blame. I thought I would share this case from Tort Law, page 63:
In Stansbie v Troman  2 All ER 48 the claimant, a householder, employed the defendant, a painter. The claimant had to be absent from his house for a while and he left the defendant working there alone. Later, the defendant went out for two hours leaving the front door unlocked. He had been warned by the claimant to lock the door whenever he left the house.
While the house was empty someone entered it by the unlocked front door and stole some of the claimant's posessions. The defendant was held liable for the claimant's loss for, although the criminal action of a third party was involved, the possibility of theft from an unlocked house was one which should have occurred to the defendant.
So, the painter was liable. However, that doesn't let the thief off the hook. If the police find the thief, they will still arrest, prosecute, and incarcerate him. The painter won't serve part of the thief's jail time, even though the painter was held liable in this case. So, even in the best case scenario for those claiming "negligence" for vulnerable systems, it doesn't diminish the intruder's role in the crime.