The concept of sin is largely based on morality, and what is percieved as wrong or unjust. Morality in turn is based on desired traits humans should cultivate, however, it's rather hard to pinpoint what exactly is moral and not, since morality can't really be measured, and some actions, even though they may be inspired by good will, can produce more ill effects than good effects. It is then hard to judge the person who executed such an action, since some may say he acted morally due to his good intetions, while others may argue he acted immorally due to the effects of his actions. Rather than "sin and punishment" one could argue that there is balance in the universe, due to which one will have all his decisions/actions/thoughts/etc. "balanced out" and returned to him in equal quantity and quality, i.e. karma. This doesn't mean that he is punished or rewarded for his actions, just that his actions have a consequence, which will have a direct effect on the initiatior of the action at one point in his life, the afterlife or even any of his future lives. What goes around, comes around, in other words.