Presumption of innocence is reasonable because most people are innocent. It is not because the world is imperfect. It follows from the base rate, which is experimental, not from any fundamental principle.

For example, if most officials are corrupt, you should not presume the official you are dealing with is not corrupt. That's just stupid. Legal case still should be backed by evidence, but your personal presumption should consider the base rate, not just presumption of innocence.