It is not good for the one who makes the laws to execute them.
Gist of Idea
Law makers and law implementers should be separate
Jean-Jacques Rousseau (The Social Contract (tr Cress) , III.04)
He doesn't give his reasons here, but this piece of wisdom is widely supported. There is a problem when the executive find themselves trying to enforce bad, discredited laws. Maybe the police know best what the law should say? Or not!
Rousseau,Jean-Jacques: 'The Basic Political Writings', ed/tr. Cress,Donald A. [Hackett 1987], p.179