Sorry to disagree with you on that. There is a long and well-established line of cases in all of the states that precludes you from doing it. It's called "intentional interference with a contract." Do a Google on it, and you'll see.
But you are right that if all they did was exercise their freedom of speech, then that makes it harder to sue. Not impossible, though.
True enough, you can sue for anything. I just don't see any grounds to sue the guy who told. If you're writing a web column, by what am I supposedly bound by that prevents or should prevent me from divulging (to anyone) to anyone the details of your column? Even if you used a screen-name, and my understanding is that this guy used his real name, I don't see the problem. When you write something, and put it up in a public forum, you have to assume it's well...public.
Yet, you seem to think that the guy who told did something wrong. I can't fathom that. He brought a column that was posted on a public forum to the attention of an individual? It's almost scary that you find that actionable. Is there something I'm missing here? I hope so.