And I can imagine there would have been such an outrage if it had been Alexandra Marcus', and not Alexander Marcus' head that was crushed by Khan.
I don't know the answer to this. But I can't imagine it wouldn't have raised a few eye-brows here in the States.
The problem is, you can't have it both ways. If Admiral Marcus had been a woman, and if the story moves in a way that called for Khan to kill her in a fit of rage for the wrongs he thinks she did to him, then it has to be done. So it comes down to this, does he crush her head or do something "less violent," like vaporize her with a phaser or poison her?
For what it's worth, no one seemed too upset with what happened to the Borg queen or the Duras sisters.