Blatant sexism makes no sense

Tell me if this is sexist:

-- Sexism test begins --
Feeny gives the class an assignment about projecting the future - what job will you have, what will your family be like and so on, and everyone has to present it to the teacher (with appropriate cosplay, it seems). So far, so good.

Corey then marches to Feeny and tells him he (Corey) is now the president, and he has abolished this and that and blahblah. Feeny says that Corey's future world seems to be a very peaceful and loving one (not correcting the obvious unrealistic bits at all), to which Corey replies something like:

- Yes, especially since we've moved all women underground and use them just for breeding.

(Crowd roars of laughter and applauds hard, Feeny doesn't react almost at all, and moves on to the next student, as if this is a normal statement that needs no correction or notes of any kind)
-- Sexism test ends --

Now, did anyone find that to be weirdly and blatantly sexist?

Of course this is not EXACTLY how it happened in the show - the quote is otherwise correct (word-for-word), but instead of Corey, it's Topanga that says that, and instead of women, it's men that are forced to live underground as sex slaves without daylight or any hope to do anything except breeding.

Do you suddenly find this not sexist? I mean, sexism goes both ways, you can't have one gender be attacked and call it sexism, while calling doing the same to the opposite gender normal.

Yet this kind of blatant sexism is everywhere in the media, especially in these popular, high-profile shows.

Seinfeld has another example; let's check it out as long as we're doing this..

Jerry is going to his friend's 'gay wedding'. Someone asks him if he's gay. Jerry responds: "No! I hate women, but I am not gay."

Does this sound like a normal, non-sexist thing to say? Of course not.

Obviously this was also done by Elaine, not Jerry, and the word 'women' was actually 'men' - so now it's suddenly OK?

Doing the gender reverse-trick reveals SO much about how much it is OK to hate 50% of humanity based PURELY on their body, their genitalia, but not the other half. The other half you are not allowed to EVEN treat neutrally, and you can ACTUALLY now go to jail if you 'disrespect' that pedestalized half. (Look it up, it's some kind of weird legal system in Scotland or some other strange land like that)

This world is getting crazier every day, but watching these old TV shows, we can see it HAS been insane for a very long time, but people have just been blind to this BLATANT SEXISM that's everywhere.

Hate men? Perfectly OK, funny, let's all laugh, clap and roar and celebrate.

Hate women? HOW DARE YOU! Go to JAIL for 7 years!

(Sadly, that's not even an exaggeration..)

None of this makes any sense; let's either be sexist to both genders (though aren't there million of them and simultaneously, HOW can sexist even against women exist when 1) Gender is just a social construction and b) No one can define what a woman even is?), or let's stop sexism against men just as much as we are trying to stop sexism against women.

Otherwise, equality of HUMANS can never happen, why is it OK for 50% of humanity to be downtrodden and laughed at and vilified completely just because of their genitalia? Isn't that called prejudice, sexism, a hate crime? And yet people and these shows do it openly, blatanatly and completely insanely.