Heh. The system is designed to tolerate a certain amount of abuse of discretion, on the fiction that prosecutors are nominally honest.
"Equal protection" has the same validity as "objective press."
14th Amendment sec 1: ...nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.
This is enforceable in a civil action under 42 US Code Chapter 1.