As we all know, witnesses routinely share in gossiping, slandering or maligning the name and reputation of those who are "spiritually weak" or ones who "fade" or "stop associating".
They feel it is ok to speak badly of such ones who "have left Jehovah's organization".
Of course, some of the worst perpetrators of this are Elders and their wives, who insidiously plant negative stories in the minds of all they interact with in the congregation. They may never have actual facts, but since when do facts matter to witnesses?
However through such conduct they manage to separate people from one another, or cause rifts amongst former friends.
This sort of conduct is plainly inappropriate.
But what scriptures could be used if the opportunity arose to confront such ones about the way they have behaved?
New Living Translation James 3:5
In the same way, the tongue is a small thing that makes grand speeches. But a tiny spark can set a great forest on fire.
Aramaic Bible in Plain English Proverbs 26:17
He that meddles in a case that is not his is like he that takes a dog by its ears.
Feel free to add other scriptures that come to mind.