For me this is about equality, not for the characters but for the actors. In almost all professions you could sue for damages if you were refused a job on the grounds of your sex. Acting gets a pass because, with a few exceptions, it would be silly for a woman to sue because she didn't get the part of a male character. The sexism comes in because they don't write parts for women in the first place.
Sure, good point.
Action movies certainly do skew male. It's a shame that the excellent precedent set by Alien
somehow didn't carry the momentum forward.
Action movies do seem to be getting more and more female characters, but they tend towards the gorgeous, buxom kick-butt Boris Vallejo variety of mens' fantasies. Not as much variation as you get with male heroes.
For all that I am happy with the male cast we already have, and I wasn't too fussed either way about Carol Marcus (would prefer her screen time going to Bones, Sulu or Chekov) I did think Alice Eve was an awesome chick, heaps of fun on the interview circuit and should make a fun addition to the cast (as long as it doesn't degenerate into both Kirk and Spock with girlfriend troubles
As someone said upthread, Admiral Marcus could easily have been a female character.