What's the difference between bitching about people and morally judging people?

I take the virtue of justice seriously: I try to be careful and objective in my moral judgments of others, and then I act on those judgments. However, I've found that most people don't do that. Instead, they bitch about other people out of annoyance, including about serious wrongs, but then continue to deal with those people as before, perhaps after a cooling-off period. I hate to listen to these unserious and often unjust complaints about others, and I don't relish the thought of people complaining about me in that way to others. How can I explain my objections to such bitching in a friendly way? How can I avoid being bitched-to or bitched-about?