With sincere repect to Professor Mezey, it's not as simple as he makes out. In the 17th and 18th Century, many fine writers and educated people used "they" as a singular, gender-neutral pronoun.
And the word "man," though people often said it included women, was quite often used in contexts that show otherwise. In fact, the generic use of "he" and "man" was sufficiently murky in 1850 that the British Parliament saw the need to pass a law saying "words importing the masculine gender shall be deemed and taken to include females." Why would such a law have been necessary in 1850 if the question was as clear as Professor Mezey now claims?
And Edmund Burke, a rather grammatic fellow, didn't think the word "man" included the word "woman" when he wrote of the French Revolution "Such a deplorable havoc is made in the minds of men (both sexes) in France. . . ." It seems rather clear that he did not feel that simply saying "men" would make it clear to people that women were also intended in his meaning.
In those occasions when the author did not take pains to show that "man" includes "women," we often find that confusion resulted. In 1879, women doctors were excluded from a prestigious medical society because the by-laws on membership used the pronoun "he", which was deemed to exclude women. If "man" includes both genders, why did the medical society feel that its use excluded women?
I've read lots of this kind of thing before, but right now I'm relying on
http://www.english.upenn.edu/~cjacobso/gender.html. The article also points out some other interesting oddities regarding gender speech, such as the medical research report entitled "Development of the Uterus in Rats, Guinea Pigs, and Men," which is good for a chuckle. And the article provides the following sentence, which I presume most people would find a bit odd: "A doctor is a busy person; he must be able to balance a million obligations at once. Dr. Jones is no exception, with a clinic to run, medical students to supervise, and a husband with polio."
Professor Mezey's version of gender in language corresponds to the unexamined orthodoxy of the grammarians who held sway when Professor Mezey was learning grammar, but it overlooks much of the history of usage in English and it also overlooks the fact that millions of people these days, unlike Professor Mezey, no longer hear the gender inclusiveness of "man" even assuming that most people used to hear it...and that is somewhat in doubt.
I'd further add that a usage can be offensive even if it is accepted usage and blessed by grammarians. From curse words to racial epithets, there are words that are "validated" by usage but that people can nonetheless object to and ask people not to use. In the case of gender, however, we're not just dealing with modern PC sensibilities but a centuries' long history that actually validates the singular neutral use of "they" and rejects the notion that "man" includes "woman."
[This message has been edited by Roger Slater (edited July 15, 2002).]