Explain the difficulties with arguments based on self-defense

Self-defense is a widely accepted exception to the "thou shalt not kill" proscription. Generally, it is held that if someone is trying to kill you, and the only way in which you can save yourself is by killing the other person first, that action of defense is justifiable. Some have used the self-defense argument as a reason to allow abortions in cases where the mother's life is endangered by the pregnancy. Others refute this by pointing out that self-defense is permissible only when the attacker is intending to kill you. If a hungry lion was attacking you, it would not be permissible to throw others in its path so as to satiate its hunger and escape being eaten.