Because then the government just votes laws "everyone who wears shoes or breathes goes to prison for 10 years" and as long as they control the prosecutor genera

Because then the government just votes laws "everyone who wears shoes or breathes goes to prison for 10 years" and as long as they control the prosecutor general, they just imprison anyone they want. In other words, if you don't have fair and honest application of law (ie. the prosecutor going after every case they know about), NOT having law at all is actually preferable.