You fail to appreciate the value of our adversarial legal system as a check on tyranny and overzealous prosecution.
In the system you propose, attorneys would essentially serve as agents of the court, working with the judge to discover the truth. But they too would have imperfect judgment. If accused people knew they could not trust their attorneys, everyone--guilty or not--would proclaim their innocence. Every attorney would be forced to guess at his client's innocence, and the quality of defense that client received would depend on that guess. An attorney would invariably make a mistake occasionally, and believing an innocent client to be lying, follow your advice and see that the "truth" come out at trial giving him the sentence he "deserves." The very thing that you decry in this thread--the conviction of innocent people--would be more common.
Imagine if you were falsely accused and your own attorney didn't seem to believe you. In the current system, you could count on the fact that he would still do his best to get you acquitted. In your system, you would be SOL.
If that isn't enough, I'll point out that Germany--hardly famous for its long history of protecting innocent people against overzealous governments--has a legal system more like the one you advocate. The Anglo-American common law system--complete with the adversarial approach we have now--has been one of the strongest bulwarks against tyranny the world has ever known.
In the system you propose, attorneys would essentially serve as agents of the court, working with the judge to discover the truth. But they too would have imperfect judgment. If accused people knew they could not trust their attorneys, everyone—guilty or not—would proclaim their innocence. Every attorney would be forced to guess at his client’s innocence, and the quality of defense that client received would depend on that guess. An attorney would invariably make a mistake occasionally, and believing an innocent client to be lying, follow your advice and see that the “truth” come out at trial giving him the sentence he “deserves.” The very thing that you decry in this thread—the conviction of innocent people—would be more common.
The adversarial system should still not allow situations like this one to occur. What kind of ethics would keep this lawyer from insisting that his client’s confession be given to the jury? Only a lawyer could define ethics in such a manner. The current system gives too much control of evidence to the judge and lets myriads of criminals off on technicalities.