To his credit, he did sort of do that, about a year ago.
"I got wrong that the creative class could magically restore our cities, become a new middle class like my father's, and we were going to live happily forever after," Florida said. "I could not have anticipated among all this urban growth and revival that there was a dark side to the urban creative revolution, a very deep dark side."
http://www.houstonchronicle.com/business/texanomics/article/...
So I'd say this isn't an ad hominem. I'm not trying to attack the argument by attacking the man. I'm just attacking the man. Florida in particular isn't credible because a decade ago he was boosting municipal gold-digging -- chasing after high-flying tech companies and ignoring bread and butter issues like the ones he's lately rediscovered.