The chain of thought that goes
I only prosecute worthy cases
=> I picked those cases because these people are guilty,
and need to be convicted for the good of society
=> my conviction rate is exactly the same as my
'I made a better world' rate.
If the conviction rate is low, people on the Internet say that the prosecutor is just harassing innocent people.
If the conviction rate is high, people on the Internet say that the judges rubber-stamp whatever the prosecutor throws at them.
I've never seen anyone say "sounds about right" when any conviction rate was posted.
[Edit: Killed the last sentence, as per site guidelines]
It's like the story about communist strategies for optimizing production, making a metric by which you measure performance in some hard to quantify domain is going to give you an industry optimizing for that metric which will have a ton of un-intended consequences.
The goal of a prosecutor should not be to aim for a certain conviction rate (either high, low or anything inbetween) and the goal of a justice system should not be related to any such metrics either.
The right way to go about this would be to establish guilt or innocence without regards to any metrics and with a relative disregard for the cost of such an operation because the number of criminals is low compared to the number of non-criminals and should err on the side of caution.
You mean besides obvious empirical observation of the system's history in the past 50 years or so?
Can you please back up your bold statement that the system attracts personalities driven by their own ambition with some data or evidence?
I'm intimate with a number of prosecutors (including my partner), and I've not once come across a prosecutor who possesses such attributes of character. It's quite the opposite actually - most turn away higher paying law firm jobs to do what they believe is community service.
To me this injustice has occured on behalf of corrections facilities management. Very sad.