Extra Note on Supernatural: Sexism and the Fandom

I know that I wrote a lot about the sexism of the show itself, but I didn't touch on the fandom. TV shows are heavily reliant on returning viewers and so the writers watch how the fandom reacts to the introduction of new characters and then deal with the new characters accordingly. If the fans love a character, we're likely to see a lot more of him or her. If the fans hate a character, they will die or leave pretty quickly. This has definitely been a contributing factor to the lack of women on Supernatural. Remember Bela Talbot?

They introduced her and the fans hated her. So they killed her off. (I will admit that she annoyed me too, but I wouldn't necessarily have killed her off.)
And the uproar over the attraction between Meg and Castiel was mostly directed at the character of Meg. Rather than just saying that they felt the relationship was contrived and unimportant, a large part of the fanbase went after Meg. I personally felt that the later Megstiel interaction was a bit of a contrived "no homo" moment given the relative lack of continuous relationship development, but I do love Meg as a character.

He learned that from the Pizza man.

I think that a lot of this hate for female characters is derived from the worry that they will all become romantic interests for Sam, Dean, or Cas and separate one of them from the core storyline of man-pain. Perhaps this is why Charlie is so beloved; her sexual orientation makes her a non-threat to the Sam-Dean relationship or to Destiel.
So while it is true that the show does show some distinct sexism, they are utterly dependent on the support of their fanbase, and that fanbase treats the female characters like shit. Maybe if we treated the women they gave us better, we'd get more women... Let's try that, next time.