Slander is a prohibition in the Torah. There are exceptions like when you need to warn someone about a dangerous person. But as a starting point, one needs very urgent and good reason to be able to disparage another person. [I mean the starting position is never to say something negative about another person. Then based on circumstances, there might be a need and even a requirement to say something.]

One of the secrets of success I always thought that the Mir Yeshiva in NY had was the morning session where people would learn the laws of slander after the morning prayers. So there was a great awareness of the issues involved in speaking slander.

Just for clarity:

Lashon Hara can be just saying something negative --but is worse if it is with intention to cause damage or even can cause damage.  It is divided into בין אדם למקום ובין אדם לחבירו and the laws are different. For between man and God issues it is enough if the person is on that path in a constant way. Just just an accidental sin. Then one can say lashon hara and warn others. For issues between man and his fellow man, that is where you need some conditions to be able to say anything negative: for benefit, to see it oneself, rebuke, no other way to get that benefit, to be clear that what one think happened really did happen, it will not cause more damage that would come to the person if he was tried in court, that it really is clear according to the laws of the Torah.

Some examples: it would be forbidden for a woman to lie about her husband in court in order to get more money out of an alimony case. There are lot of reasons for that. One is that Lashon Hara even on true things still needs lots of conditions. All the more so lying about something is worse. And here it is with intention to cause damage.