The people who designed the jury system had all the formal law education you ask for.

The idea is that such decisions are not mere technical matters, and the law is not for some "supposedly" impartial technocrats to impose their opinion on, but to reflect what society thinks.

After all it's not some god given or mathematically derived laws that need to be applied, the law is the will of the sovereign people (with some intermediaries as they can't all just draft them together).

Besides the jury system works just fine in other countries.

It's the:

- systemic racism,

- bad incentives for DAs (and political careers associated with being one),

- strict adherence to the letter of the law when the spirit is clearly elsewhere (e.g. judges not freeing people for some technical BS despite full evidence that clears them)

- privatization of the prison system and large interests

- Old Testament-style vengefulness (e.g. death penalty? In 2018? Third world prison conditions? Long term torture-level isolation?)

that breaks down the US justice system.