i do wonder why esperanto uses male as standard
ex)knabo(male) + in = knabino
like this, you put some words in male nouns to make female nouns. why?????????
and if gepatroj is right, shouldn't be gepatrinoj right????

Why is it the default? Well, for multiple reasons, perhaps the simplest one being that Zamenhof lived in a fairly patriarchial society and was a product of his time. It was normal then to think of male as being the 'default' status. In any case, the purpose of -in- is to reduce the vocabulary burden - you no longer have to learn separate roots for "mother" and "father", "aunt" and "uncle", etc.

In modern usage, however, the supposedly "male" default form is generally considered gender-neutral, with the exception of family terms (patro, avo, nepo, etc) and a handful of other words like "viro". "Knabo" could thus be used to refer to a girl as well as a boy, depending on the context (though "knabino" is recommended if you wanted to clarify or emphasise the gender). EDIT: My mistake, I was thinking of 'infano' here. Knabo is decidedly not one of the gender-neutral terms, at least according to standard usage.

"Gepatrinoj" isn't used because "ge-" attaches to the main stem of the word, which is "patr-". The "-in" suffix is thus simply unnecessary - it doesn't add anything to the meaning, we are already informed by ge- that both genders are present. I suppose it's semantically valid, just very unusual.

Some people don't like that convention, so instead they assume that everything is genderless and then use other means to mark male gender.

Some use "vir-" and some use "-icx" so a rooster might be called "virkoko" or "kokicxo".

Nile:Some people don't like that convention, so instead they assume that everything is genderless and then use other means to mark male gender.

Some use "vir-" and some use "-icx" so a rooster might be called "virkoko" or "kokicxo".

Counting the seconds until novatago intervenes ranting …

It is that way because Zamenhof lived in a time where a patriarchal society was the standard.

Regarding the "iĉ"-affair. Most other languages are like that anyways, using "iĉ" is the same as refusing to use the word "woman" because it contains the word "man". Or German speakers freaking out if people use the word "eine Lehrerin" (female teacher) derived from the word "ein Lehrer". Or in Norwegian "ei lærerinne" derived from "en lærer" and so on and so on...

People may of course do as they like, but know that endless tinkering with our language will only weaken it, and its position. People learning the language will be insecure and confused as to what is right when not even the 2 million speakers of it can agree to a norm.

The way that most people do it these days are:
Bovo might be a cow or a bull, bovino is a cow, virbovo can be used for a bull.

Viro is a man, not a person which gender is not known. Virino is a woman. Viriĉo is nothing.
The problem with people doing this in Esperanto is that the Esperanto learning group is a huge percentage of the Esperanto you will find online, few people speak it as their native language so it is easy for the people coming up with ideas like "iĉ" to target the learners, even going as far as to use it in learning books without stating that it is a neologism and not the norm. This is contrary to feminists refusing to use the word woman and rather using words like Womon and Wymyn who does not have the opportunity to implant their words in any learning material people will actually use.

vikungen:… Regarding the "iĉ"-affair. Most other languages are like that anyways, using "iĉ" is the same as refusing to use the word "woman" because it contains the word "man" …

Naa, that's not the same issue. Let's look at the etymology of the word "woman": It originated from the word "wifman", which is composed out of the words "wif" (female) and "man" (human). So actually "woman" really means "female human".

vikungen:… Or German speakers freaking out if people use the word "eine Lehrerin" (female teacher) derived from the word "ein Lehrer" …

Um… I don't see any reason the freak out due to using this form.

vikungen:… Or in Norwegian "ei lærerinne" derived from "en lærer" and so on and so on …

Waaaah, Nynorsk!!

There is no doubt that there are issues both ideological and grammatical that could be addressed by proposing changes to Esperanto. However, as the language stands, it works, as anyone who has used it in an international setting knows.

Por ke lingvo internacia povu bone kaj regule progresadi kaj por ke ĝi havu plenan certecon, ke ĝi neniam disfalos kaj ia facilanima paŝo de ĝiaj amikoj estontaj ne detruos la laborojn de ĝiaj amikoj estintaj, ― estas plej necesa antaŭ ĉio unu kondiĉo: la ekzistado de klare difinita, neniam tuŝebla kaj neniam ŝanĝebla Fundamento de la lingvo. Kiam nia lingvo estos oficiale akceptita de la registaroj de la plej ĉefaj regnoj kaj tiuj ĉi registaroj per speciala leĝo garantios al Esperanto tute certan vivon kaj uzatecon kaj plenan sendanĝerecon kontraŭ ĉiuj personaj kapricoj aŭ disputoj, tiam aŭtoritata komitato, interkonsente elektita de tiuj registaroj, havos la rajton fari en la fundamento de la lingvo unu fojon por ĉiam ĉiujn deziritajn ŝanĝojn, se tiaj ŝanĝoj montriĝos necesaj; sed ĝis tiu tempo la fundamento de Esperanto devas plej severe resti absolute senŝanĝa, ĉar severa netuŝebleco de nia fundamento estas la plej grava kaŭzo de nia ĝisnuna progresado kaj la plej grava kondiĉo por nia regula kaj paca progresado estonta.

L. ZAMENHOF.
Varsovio, Julio 1905.

While we await this international recognition, the above will be good enough for me.

malglatamelo:
L. ZAMENHOF.
Varsovio, Julio 1905.

That old guy? He was so malmojosa. In fact, he didn't even know the word "mojosa".

Bruso:

malglatamelo:
L. ZAMENHOF.
Varsovio, Julio 1905.

That old guy? He was so malmojosa. In fact, he didn't even know the word "mojosa".

True, but it isn't a fundamental problem...

Tempodivalse:In modern usage, however, the supposedly "male" default form is generally considered gender-neutral, with the exception of family terms (patro, avo, nepo, etc) and a handful of other words like "viro". "Knabo" could thus be used to refer to a girl as well as a boy, depending on the context (though "knabino" is recommended if you wanted to clarify or emphasise the gender).

No, "knabo" is just like "viro"; it is specifically male. If you want a term that can be a boy or girl, use "infano" or "junulo" (which last is, as far as I know, somewhat more likely to be considered male by default, but can be either, or so I'm told. At any rate, PIV doesn't say anything about "-ul" being male).