While I agree, that is a rule of thumb, a heuristic. Properly considered, an act truly devoid of any intention is a mere reflex with as much moral weight as an act of nature. And I have in the past written about the morality of a physical reflex which ends up killing people - I could dig up the post, but the gist of it is that I don’t believe you are culpable. That’s why there are lesser punishments for negligence; negligence is a different act.
For the purposes of decision making, morality is relative. If one choice is the most morally positive, it is the moral choice. And as I wrote above, you always have a choice. Even when you are “forced” by the circumstances to do a horrible thing, that means you think the circumstances justify (moralize) what would in other circumstances be an immoral act. To wit, if killing a person is the most morally positive choice, then killing that person becomes moral.
~Max