As long as he was peddling magical dietary supplements and weight loss pills he was a lovable scamp and was allowed to carry on with his mischief. But as soon as he dared cross Monsanto, he is a quack that must be squashed.
Here's the relevant portions of the letter in question:
As described here and here, as well as in other publications, Dr. Oz has repeatedly shown disdain for science and for evidence-based medicine, as well as baseless and relentless opposition to the genetic engineering of food crops. Worst of all, he has manifested an egregious lack of integrity by promoting quack treatments and cures in the interest of personal financial gain.
Thus, Dr. Oz is guilty of either outrageous conflicts of interest or flawed judgements about what constitutes appropriate medical treatments, or both. Whatever the nature of his pathology, members of the public are being misled and endangered, which makes Dr. Oz's presence on the faculty of a prestigious medical institution unacceptable.
I see one reference to GMO opposition and two or three references to quack science and conflicts of interest. Dr. Oz's rebuttal on the other hand only specifically mentions the GMO's.
It's a clever PR ploy on Dr. Oz's part, focus on the milder part of the accusation and suggest a conspiracy. Meanwhile ignore the more serious accusations that are much harder to defend.