A high or low IQ doesn't necessarily translate into how well you understand how your actions affect others.
A low IQ individual is more likely to lack impulse control and act based on extremely short-sighted motives, like an animal.
This also isn't a legal matter - it's a moral one.
The legal system is an attempt to codify our (consensus) moral intuition. Why does the legal system attempt to weigh "motive" and "free-will" unless those concepts inform "morality"? Why are you hair-splitting? Do you believe the law should also be moral?
Your motives play a large part in determining whether you acted immorally or not.
That seems ok for crimes that are directed acts of violence, (
like a dog attack) but what about crimes of negligence?
[The clip shows a dog getting shot with a bb gun and immediately attacking its owner, wrongfully jumping to the conclusion that the owner was the cause of the pain the dog felt as a result of the shot, completely oblivious to the sniper fifty yards away.]
Taking something from someone while not knowing it belonged to anyone is not the same as deliberately stealing from someone.
But wouldn't you have to have the mind of a child (or an animal) to believe that something of value had no (likely) owner?
(IFF) free-will is proportional to intelligence (animals have less, humans have more)
(AND) free-will is proportional to moral culpability (without free-will there is no moral culpability)
(THEN) intelligence is proportional to moral culpability.
Please feel free to modify any of the above statements to better fit your "moral intuition".