The Netziv has an insightful comment on the juxtaposition of the prohibition of rechilus with the command not to stand by idly and watch another's blood get spilled (19:16). On the one hand, we are commanded to respect confidentiality, privacy, and not speak evil about others. On the other hand, at times a failure to speak out can lead to great harm, to blood being spilled or other heinous crimes being committed and perpetuated. The laws of lashon hara are not meant to enforce a passive silence in the face of evil.
The Netziv captures in these few lines the tension between competing values that I don't think we as a community have fully figured out a way to resolve. Unfortunately the topic is far too often relevant to current events. A newspaper story or blog post appears about some person, often an individual of note, who is accused of crime: How do we ensure that the accused is not unjustly slandered and made the victim of baseless rumor while at the same time avoiding silence in the face of potential criminal action? How do we balance our obligation to respect the rights of the not-yet-proven-guilty with our obligation to protect the innocent from harm? When details of the sordid details are published, do we close our eyes and ears under the guise of avoiding rechilus, or do we spread the word based on lo ta'amod al dam rei'echa?