There should never be a law passed that gives the head of states immunity from persecution. If a head of states commits a horrible crime, they need to be punished for their actions, even though they are the head of state. If they are given immunity, then they will become out of control.
No one should be above the law, especially leaders who swear to uphold the very laws they cherish. Immunity should not be given to heads of state, otherwise they may be tempted to break laws just because they can. Immunity sets a dangerous precedent for future leaders of a particular nation--where does the immunity stop? Will it stop with rape or murder? What are the limits of these immunity laws?