Actually, it was Lou DiBella who ruined Jermain Taylor.
Truth be told, physically, Jermain Taylor can still fight. Despite being stopped by Abraham, Froch and Pavlik, he was actually doing pretty good and in every one of those fights...he was never dominated from pillar to post. In my opinion, I don't even think he needs to "retire" because, outside of the last one, none of those knockout losses were really that brutal.
Jermain Taylor's mental state of mind, however, is what was ruined by DiBella the minute he put him on the fast track to a world title. You gotta have the mental state of mind to go with your physical attributes, and sadly, that's just not something that Taylor was ever given the opportunity to develop. Some guys are born with that kind of mental toughness...others have to develop it. Taylor, obviously, was one of those who had to develop it and the minute he was finally starting to put it together (around the time of the Joppy fight), DiBella decided to put him with one of the most cerebral fighters in the game. Dumb, dumb, DUMB move! Taylor may have "won" those fights against Hopkins, but you can tell at the end of those fights that mentally, the doubts were creeping back in to Taylor's head. His next couple of fights (Spinks, Ouma and Wright) only added to the unraveling of his mental state of mind. With each of those fights being close and so many people saying the other guys (mainly just Wright and Spinks) deserved the victory, it's no wonder that Taylor began to seriously doubt his abilities. It all came to a head in the Pavlik fight, when he was able to put Pavlik down, but not away...from there, it was just a fast track all down hill.
But it wasn't just one particular fighter that "ruined" Taylor...it was a combination of all of those fights that basically killed Taylor's mental state of mind. But if you have to put the blame on one person, it would be his promoter, Lou DiBella, who's only job is to guide his career and build him up the right way. That's just not something that Lou DiBella knows how to do. Whatever he wants, the man wants it fast and now and that's how DiBella treats his fighters. And don't think that Taylor is the only one. Paulie Malignaggi is another fighter that Lou did that too (i.e. the Miguel Cotto bout)...and Andre Berto will likely suffer the same fate as Jermain Taylor if he himself is not wary of any offers made by DiBella.
Just my two cents on the whole subject, but I'm quite sure there's going to be a lot more revealed about Lou DiBella in the very near future on the front page of FightHype.com.