This saying is a caution against taking things like little slights and inconveniences personally and holding grudges. It is not meant to imply that it is unwise to assume that a person caught in a criminal act intended to be committing a criminal act.

This application of the maxim relies on fallacious logic. Ego, ignorance, incompetence, and malice are not mutually exclusive properties, but even if they were, motivation is irrelevant in matters of law and order.

Ignorance of the law does not render the law unbroken. It doesn't matter if a drunk driver maliciously mows down a pedestrian, or if they in their ignorance allowed their ego to convince them that they were capable of driving in their condition. The person who was hit by the car is just as injured, and the driver is just as responsible for the outcome.