Throughout the Bible there are multiple references to the sinfulness of gossip, the passing on of malicious details, speculations, and falsehoods. The problem of gossip is taken very seriously in the Bible, and there are sanctions against those who gossip.
Yet gossip is the bread-and-butter of interpersonal discourse for many people, most of the time - including Christians. And it is the very basis and substance of much mass media communication, which has expanded so much in recent decades.
And the synergistic combination of interpersonal discourse with internet mass media has made the phenomenon of social networking into by far the largest and most powerful international malicious gossip fest that there has ever been in the history of the world.
So, there is a serious, damaging sin - which is rampantly growing, combined with little awareness of the gross wickedness involved.
An example from a while ago was the Christian-driven gossip, ignorance and lying directed against the Harry Potter books and JK Rowling. This matter is thoroughly dealt with by Jerram Barrs in the following lecture.
As so often, people are most in danger of unrestrained sin when they feel they are being self-righteous.
Obviously malicious gossip is - sooner or later - sickening for decent people, they feel disgust for themselves and others. Moralistic gossip is the worst kind of gossip, people hatred, spite and malice are disguised.
The matter of gossip is not to be confused with 'judgement' - and especially not with the confused and mistaken idea among Christians that humans are (supposedly) not allowed to judge the sinfulness of others.
This is nonsense - the judgement from which Christians are supposed to refrain is that concerned with their ultimate salvation. But it would be insane and indeed wicked for humans to refrain from judging one another about their activities and motivations - of course we must judge!
So, as always, extremes are both wrong. Gossip is certainly a sin; but we must judge, and may have a duty to warn others in light of our judgements.
Part of doing right is a matter of motivation (real inner motivation, not what you might say to others to justify yourself); and part of it is a matter of knowledge based on trusted sources and persona experience; versus passing-on hearsay from sources known to be dishonest, spiteful, destructive and themselves wicked.