R' Nachman opens his famous "azamra" torah (Likutei Moharan 282, link) by explaining the pasuk, "V'od me'at v'ain rasha,v'hisbonanta al mekomo v'einenu." Every person has some good in him/her. By finding that goodness and judging another favorably, the individual being judged is actually transformed into a better person. "V'od me'at," if you can find just that little bit of good, then "v'ain rasha," the rasha will be no more. (R' Nachman goes on to say that this applies not just to others, but to oneself as well. It is easy to fall into despair and feel that one's avodah has no value, but this road of despair leads to becoming a rasha. One needs to remind oneself that every drop of avodah has value to Hashem -- there is no greater motivator).
My wife suggested that this idea may also be alluded to in the expression, "Emor me'at v'aseh harbeh." If one speaks about and praises that "me'at" of goodness that can be found even in the rasha, it will produce enormous results, "v'aseh harbeh."