Think about it in wider terms though - If you murdered someone, then said I was never told that was wrong - then does it make it ok ? Ok if the person is mentally unstable and are physically incapable of knowing right from wrong then they are still guilty of the crime but would have mitigating circumstances at sentencing (they would actually plead for man-slaughter, as murder carries a guaranteed life sentence - where man-slaughter mitigation can be taken into account).

Anyway why should someone who has been educated about right and wrong and knows what right on the road be punished more than someone who hasn't bothered to learn or be told ?