Prosecutional discretion is legalized bigotry. The legal system has a strong history of allowing sexist, racist, and classist thought to drive how laws are enforced. Any fair or just system would allow no such discretion.
I agree that prosecutorial discretion allows racism and other prejudice to be reflected in enforcement. However, every practical system will have prosecutorial discretion because resources are always limited.
Except, Congress's ability to create a never-ending stream of new laws seems to be limitless. Maybe we should require a 3/4 majority and "slow" process to create a law but only a 1/4 minority and fast track needed to repeal one.