Fine. How would you deal with the forensics people deliberately presenting DNA evidence that never existed?

Heard about the FBI and their recent DNA scandal. Our current system isn't preventing the problem already. Police already are known for falsifying evidence.

As for a legal basis, you still have the ability to sign away your rights (well some of them at least), which is how an NDA would still be legal. You can choose to enter into such a contract with the government, but with the key difference being one of choice. You don't choose it, then you don't get to be a police officer, judge, etc.

Suddenly you turn a mostly reliable court procedure into one where literally nothing said by anyone can be trusted. Sure, eyewitness testimony can be unreliable, but there's no need to turn it into a kangaroo court.

It already is for the majority of the players too poor to pay to win.