That's just someone using their knowledge to be mean...

Just like a doctor, lawyer, or any other human services professional could...

Professional ethics don't require folks to be nice in their personal lives.

As for abuse, well, if they're physically abusive, it would be a reportable, actionable crime just as it would for anyone else committing it.

If there is slander that damages livelihood or such, there might be a lawsuit in there somewhere I suppose, but it's expensive and difficult in many cases to pursue something like that.

If it's basically just someone saying manipulative, uncaring, false things, that's just someone to avoid.