The person was able to hurt me because he, through a certain station, had the credibility that made what he might say about other people (such as me) matter. His opinions would be taken seriously. After taking a hit, I fixed the problem. It wasn't about vengeance. It was about doing just enough to fix the problem, then moving on. He didn't lose his job per se but I made him enough of a laughingstock that no one would take his word over anyone else's, thus making me safe from him.
After being attacked, it's not unreasonable to think that such defenses are needed in order to protect the future.
I wouldn't do that sort of thing after a "things didn't work out" situation, even if things ended badly or I got fired. I'm an adult; I'll move on. Likewise, I wouldn't retaliate against someone just for saying that I was a jerk or that he didn't like me. (Plenty of people say that I'm a jerk. That's fine.) There has to be a lot more, like fraudulent negative claims about past work performance... something that sounds objective and can be damaging... before I'm ready to fuck up someone's life. People have the right not to like me and to say that they don't; what they don't have the right to do is to deliberately damage my reputation with fraudulent or inaccurate claims.
This was a case where someone deliberately tried to damage me after I had moved far away from him. There was an act of war, and I fought back with force, and I won. I don't believe in starting fights but I do believe in ending them.