Suppose the law states that David Haroldson (or the Glorious Leader, or foreign diplomats) cannot be convicted of any crime. That's inconsistent, (perhaps) arbitrary, and unfair. Yet, it would be foolish to extend this conviction-immunity to everybody.
That can be abused as well. Just frame the leader for a crime and he sits in prison until it is proved that he is innocent, then do so again for a different crime.
For the above assume the leader is actually glorious, though of course most leaders who are called glorious are awful (IMHO)
Arguing about consistency in a system without the rule of law seems a bit foolish as well. Diplomats are a more interesting edge case. And AFAIK they can always be prosecuted and convicted in their home country.
