To What Extent Can We Overcome Prejudice?
You speak of the importance of looking for the bad in someone. I would say it depends on what looking for the bad entails.
One situation in which you could consider the question is of an employer recruiting staff. Obviously, having chosen to invite certain people for interviews, which may in have involved some biase, we can think about the whole aspect of 'bad' played out in interviews. The employee has to seek to weed out potentially good employees. This will involve a certain assessment, which will be about the person's work history and attitudes among other criteria. This does involve perceiving potential problems like to trying to eliminate people who are lazy or careless. However, on some level this can go beyond that and involve prejudiced bias, against for example gay people or married women.
It would probably be difficult to raise an official complaint for not being selected for a particular job. However, the matter is different entirely once a person has been employed. If someone is dismissed from a job it could be down to the person's standard of work or conduct, or it could involve the prejudice of the employer. It is a grey area and so many complex industrial tribunals are based on the fine lines of this matter.
I would just add that you speak of the importance of seeing bad in others in order for evolutionary survival and one -upmanship. This is once again a difficult grey area, because where does one go in separating this from bullying.