Consider the implications of usages such as the following:

• “Man is a mammal and suckles his young” – the human race is male by default; “Womankind” is a subset of “Mankind”.
• “The reader is entitled to his opinion” – if you're female, you have to pretend otherwise to read legal documents.
• “Wizard” is praise; “witch” is an insult (abuse is the only field in which there are more words to describe women).
• “The UK's greatest living author” is ambiguous; does it rule out the possibility of authoresses who are greater?

This doctrine of Male?As?Default treats women as a negligible subgroup, and femaleness as abnormal but always noteworthy.

Sexism is (in principle) avoidable in English, via words like “human, people, he/she, they”, and sex?neutral jobtitles where sex is irrelevant.  Things are different in languages with grammatical gender: e.g. in French, masculine plural is ils , feminine plural is elles , but mixed groups (even of 99 women and one grammatically masculine hornet) are ils .  To the French, Thatcher was Madame le premier ministre , masculine!  So how about Esperanto?  Surely a language without arbitrary gender?classes designed by an enlightened liberal humanist will avoid such pitfalls?  Well, uh… no.  In fact, as first propagated his brainchild was blatantly and systematically sexist.  All animate nouns were male by default, unless given the ghettoising suffix ?in .

“Boy, girl, man, woman” = knabo, knabino, viro, virino .  In English, by the way, a “virino” is a hypothetical mini?virus.  Similarly, an Esperanto job advert for a typist ( tajpisto ) would be ambiguous (how sexist is the advertiser's dialect?) without “or typistess” ( au tajpistino ).  “Father, mother” becomes patro, patrino  – dads are apparently more fundamental than mums.  Likewise, “sister” is fratino = “brotheress”, and so on with unclesses, sonesses, cousinesses, and fatheresses?in?law ( bopatrinoj ) – a sex?obsessed set of kinship terms incompatible with the systems traditionally used in many other cultures.  Vietnamese, for instance, has a common monosyllabic word em meaning “younger sibling(s)”; an idea that Esperantists need a whole phrase to express.  There is a prefix ge? to indicate “both sexes”, as in gepatroj , “parents”; but it's still a matter of some debate whether you can use it in the singular, or to refer to a group of parents who might all happen to be women.  Only one clearly neutral noun exists: “person” = homo (cf. French homme , “man”), which far from being the default is strangely avoided in coinages such as “dwarf, giant” = vireto, virego .

“Horse” = chevalo , “mare” = chevalino ; Esperanto also provides for ghirafino = “female giraffe”, blatino = “cockroachess” (“henroach”?), and so forth, regardless of tradition (English geese, cows, and ducks are female), let alone actual biology (most hornets are sterile females).  Farmers may also find handy the Esperanto “pup” suffix ?id as in chevalido , “foal”, and the “stud” prefix vir? as in virchevalo , “stallion” – but why aren't these affixes extended to humans to give words like homido = “humanling, kid” or virpatro = “father, sire”?  Too “dehumanising”?

Then again there are the derogatory affixes, fi? and ?ach , demonstrated in “Teach Yourself Esperanto” just as feminists would predict: by forming sex?specific insults.  Fivirino is “dirty woman, slut”; virinacho is “crone, contemptible female”.  Why are we never offered the male equivalents, whatever they are?  If you can't see what the fuss is about, try imagining an equivalent racist language, with black and white pronouns, a suffix ?afro , and an assumption that the human race is Caucasian (“one white, one vote”).  Now imagine the ?ach suffix being exemplified with vir?afr?acho …

Time for a few jokes.  Is a casino a feminine case?  Is a neutrino a female eunuch?  And if a fraulino is an unmarried woman, is an unmarried man a fraulo ?  Well, actually, yes; a merry jest from Dr Zamenhof.  Ha ha ha… (sob).

Even if the linguistic discrimination doesn't worry you (like two of my correspondents who explicitly supported it because it's misogynistic), this scheme of compulsory lopsided gender?agreement rules is offensive just for its poor design.  Look for instance at one of the side?effects of the rule that any affix can lead an independent life as a word in its own right: ino , “a female”; ina , “feminine”.  Generally, Esperanto requires more intricate morphology to refer to women than men; but here is an exception.  “Teach Yourself Esperanto” translates “feminine intuition” as la ina intuicio .  So… how exactly do you say “masculine intuition”?  Candidates for a masculine affix parallel to the feminine have been proposed ( ?uch, ?ab, vir?, ?ich, ?un, mal?in, ?ul ), but while few present?day Esperantists may support the original nineteenth?century system, equally few take the obvious step of marking male and female symmetrically.