The situation was so specific (and unpremeditated) that nobody (least of all Pistorius) is going to find themself in that situation again. Admittedly, it might deter somebody plotting to murder his wife, who independently thought up exactly that plan to get away with it, who will now be trying to find another cunning idea. However, it doesn't compare with (eg.) drunk driving, where many people regularly find themselves in a position where they have to apply willpower not to do it. How many people are going to find themselves suspecting that a burglar is in their bathroom and contemplating whether to shoot at the door?