If a dog is rabid, we put it down. We do not care that it wasn't the dog's fault that it was rabid. We also don't care that it didn't understand what was happening to it.
“I have long thought that the legal system’s attitude about insane murderers is itself insane.”
The Bible does not offer an insanity defense, either. Those who murder are to be put to death, regardless of their mental state.
Exceptions are given for true accidents; I am talking about deliberate murder.