Take two people: person A and person B
When person A has decided that person B is "good", for anything that person B does, person A works to understand because person A is perceiving things with "rose colored glasses". (10pm update: note, the "good" status person B may have attained is a very volatile state, and can easily turn into a perception of being "bad")
But if person A has decided that person B is "bad", everything that person B does is viewed with suspicion by person A. Person B, then, "cannot win", even if various things are done with a spirit of compassion. (10pm update: extremely difficult to move from the "bad" state to the "good" state; but not impossible)
Since I have noticed this trend, I have tried hard to examine my perceptions of what other folks are doing. I would rather not be decieved by a perception I have that may not be in line with what is really happening in the world around me. I may not always succeed in working to remain objective, but keeping it in mind helps.