Slander [lashon hara] is causing damage. That is the main issue. This fact can get obscured within all the details you find in the Hafez Haim. In lesser degrees of severity comes the points of the Hafez Haim that speaking even truth that results in damage that would not happen if judged in court is lashon hara pliss all the other conditions. [There are 7 condition altogether to be able to say something negative about someone else. In issues of between man and his fellow man. In issues of between man and God the conditions are not the same but seem to be related.]
Rehilut is different. That is causing hatred between people. That is not the same thing as lashon hara.
In any case, the point of the Hafez Haim that lashon hara is dived into between man and fellow man and man and God does not come out of this principle-of causing damage. [Causing damage to one's reputation is also causing damage.]
[There however is a sort of balance in that to warn others of to stay away from evil people is a positive command. And the prohibition of lashon hara does not forbid that. Thus the letter of excommunication of the Gra is important to abide with since it in fact warns us of danger that we would not know otherwise. In fact it would be hard to know without the warning of the Gra and Rav Shach.]
