In an essay for the New York Times Book Review, Geoff Nicholson notes that he has been called "prolific" for writing twenty books in twenty-two years, and he suspects that the adjective might be seen in some quarters as a slur.
He shouldn't let it get to him. A couple of decades ago, a psychologist named Dean Keith Simonton found a correlation between quantity and quality. In The Mating Mind (2000), Geoffrey Miller summarized Simonton's results thus:
Among competent professionals in any field, there appears to be a fairly constant probability of success in any given endeavor. Simonton's data show that excellent composers do not produce a higher proportion of excellent music than good composers—they simply produce a higher total number of works. People who achieve extreme success in any creative field are almost always extremely prolific.
If you subtract cases of early demise from tuberculosis, alcoholism, and mental illness, and handicap for poverty and/or day jobs, I bet the same would prove true of writers. Like the notion that genius is always youthful, the notion that it is always costive is myth.
It might also console Nicholson to recall that in an age when authors write blogs, only the prolific will manage to write books at all.