PDs aren't criminal defense attorneys . They have one job -- to shepherd the accused through the system and make sure the court proceedings conform to very basic constitutional requirements (like the right to cross-examine witnesses, and habeas corpus, and the protection against self-incrimination).

Formulating and providing a defense, to the extent that they do it at all, is just incidental to their primary duty. And as a PD you can't really be too aggressive about doing so, because the office of the DA essentially has the power to fire you.

If someone wants to make a real difference, the best path i s to open a private practice, and do some pro-bono criminal defense work.