Greg Smith, the ex-Goldman Sachs salesman who stunned the investment bank with a scathing public resignation in March, is now on the defense.

Smith, whose book, “Why I Left Goldman Sachs” hits bookstores today, has been facing the wrath of Goldman, media critics, and online commenters since last week, when bits and pieces of his book began to leak out and Goldman quickly jumped at the chance to characterize him as an undistinguished ex-employee with an ax to grind.

Goldman said Smith quit because he didn’t get the raise or position he wanted. It has also tried to cast doubt on the veracity of his claims by making other current and ex-Goldman employees available for media interviews to dispute Smith’s characterization of events in his book anecdotes.

Smith, a 33-year-old South Africa native and ping-pong champion, has also gotten some criticism from those who have read the book and found his story too naïve, too silly or, in some cases, too dishonest to be taken seriously.

Smith spoke with Reuters’ South Africa correspondent, David Dolan, about why he wrote the book, and responded to some criticisms from Goldman and the chattering class. He said he has received over 4,000 messages of support through email, Facebook and elsewhere since taking his concerns public in a New York Times op-ed. (Not to add another volley to this PR ping-pong game, but, in response to Smith’s response to their response, Goldman said his claims are not specific enough to investigate and that he did not respond to their repeated efforts to contact him.)