Ignoring your point about deterrence, I have issue with this: "but I insist that these people should have so much evidence pointing them to having done the act that there is no possible way that they could be innocent."

What you're asking for is a two-tiered system of guilt. In one tier the convicts are Definitely Guilty, while in the other tier the convicts are Definitely Definitely Guilty.

I don't believe a system like that is stable. Every juror who convicted Carlos DeLuna (or Cameron Todd Willingham) did so with a very firm belief in their guilt.