Over at Language Log, Mark Liberman (here) and Geoff Nunberg (here) have already set him straight. To their learned rebuttals I would like to add a commentary from Edward S. Gould, American language maven and author of "Good English" (1867).
Gould was not alone in his dislike of feminized nouns, but he devoted more space to the issue than most usage writers. He conceded that some such words (marchioness, princess) might be needed, and that others, like actress and patroness, were traditional, though "a good reason can hardly be given for their admission into our vocabulary." But many coinages, he said, were absurd, including poetess and authoress.
Poet means, simply, a person who writes poetry; and author, in the sense under consideration, a person who writes poetry or prose: not a man who writes, but a person who writes. Nothing, in either word, indicates sex; and everybody knows that the functions of both poets and authors are common to both sexes. Hence, 'authoress' and 'poetess' are superfluous ...
If, however, those two words have, by long usage, become conventionally endurable; what shall be said of the superfine affectation, prettiness, and pedantry of conductress, directress, inspectress, waitress, and so on, which have become as plenty as blackberries?
Conductor is a person who conducts; director, a person who directs; inspector, a person who inspects; waiter, a person who waits. Yet if the ess is to be a permitted or an endured addition to those words, there is no reason in language or in logic for excluding it from any noun that indicates a person; and the next editions of our dictionaries may be made complete by the addition of writeress, officeress, manageress, superintendentess, secretaryess, treasureress, singeress, walkeress, talkeress, and so on, to the end of the vocabulary.