I'm trying to follow this conversation but seeing little snippets here and there makes it tough.
Are you saying that a former employee of whatever company it is, is now an IHUB member and he now posts derogatorily about the company?
When responding to the person, I would ask him to back up his statements with facts and I would also ask him to admit publicly that he is a former employee. IMO he probably should also have that as a disclaimer in all of his posts.
If I don't have the situation correct, then just forget this post and carry on.