I respectfully disagree. While I think it is exceedingly rare that someone would knowingly choose to commit evil, if it was not possible then there would be no need to distinguish mortal from venial sin. Consider this scenario: A doctor gives a patient an inherently dangerous drug at a lethal dose. By his medical training, he knows that the drug is dangerous and that the dose is invariably lethal. Knowing this, he freely decides to do it anyway. The patient dies. He met all the necessary conditions of sin (full knowledge of grave matter, full consent, and free will), he is indisputably morally culpable for murder, and would be accordingly punished for such by the law.
Vs. this scenario:
A doctor, based on his training and the compendium of medical knowledge known at that time, makes his best judgement that a medication with known risks is necessary for a patient with a certain medical condition . The risks are deemed acceptable because the patient will certainly die without the treatment.
But there’s a mixup at the pharmacy, the pharmacist returns a prescription for a dose that is incorrect but still within the normal therapeutic range and thus not suspicious. Through a series of unfortunate misunderstandings, the doctor unwittingly gives the medication to the patient. Maybe he’s just worked two 24-hr shifts back to back because the hospital is understaffed, he’s tired and not performing at optimal capacity and doesn’t realize the error. The patient dies.
The pharmacist and the doctor could not be morally culpable for murder because the conditions aren’t met: the death of the patient was not the intention of the treatment and neither the doctor nor the pharmacist intended to kill the patient. Since there was no reason to suspect that the dose, while not inherently lethal in itself, would be harmful to this particular patient, they were not acting with full knowledge of the situation. And neither the pharmacist nor the doctor had a gun to their head forcing them to give the patient a lethal dose of medication.
BUT, they would be guilty of some degree of manslaughter or negligence. The pharmacist should have verified with the doctor that the prescription was correct no matter how routine it seemed. The chain of command should ensure that there are multiple redundancy systems in place to verify that the prescription remains unchanged from the moment the doctor orders it until it arrives to the patient. And the doctor should have realized the mistake, or recognized that in his state of fatigue he was not capable of safely performing his duties and should have excused himself from such in order to rest sufficiently.