This is an inherently subjective topic.

My understanding of what people mean by 'good' and 'bad' in a moral or absolute sense when describing some person (or thing, trend, or idea) is the degree to which the subject conforms with the judge's aesthetic. If you (or I) have a particular vision of how the world ought to work, then we think that people who work to make the real world match our idealized vision are good and people who do not are bad.

Bad people are bad because they want a world that is different than the world I want. As a subtle example, if I happen to value prompt, polite, hard working, and thoughtful people because they help me to enjoy my time, then I think that people who are perpetually tardy, or rude, or lazy, or ignorant are bad. More distinctly, if I idealize a world where subway vigilantes are able to protect themselves with their weaponry, I am more likely to think that Berny Goetz is a good person. Someone who thinks that a world full of guns is very dangerous or that usually when dark-skinned people are accused of something they are the victims of racism, will tend to think that Mr. Goetz is a murderous bigot (bad man).

The notion of 'good people' v. 'bad people' is an oversimplification and needlessly divisive. Truthfully, I believe that virtually all people are striving for goodness -- as they understand it. I might disagree with the felicity of their aims and ideals, but I try not to think of them as 'bad' or 'evil' because of it. I don't want my understanding of the issues clouded that way.