Five seconds at Google:
http://www.cbsnews.com/news/california-woman-united-airlines-changed-seat-because-gender/
IF (and that's a very big IF, as I will point out below) the story occurred AS ALLEGED (you only have one side, out of three parties - if you count the two Pakistanis as one, or four parties if you allow each one of them to have their own version), then I think all would agree that the gate agent was WAY out of line.
However, I tend to doubt the veracity of the story as presented.
You claim to fly a lot. Why don't you try the following experiment: every time you fly ask the gate agent if the person assigned the seat next to you is a male or female, and report back on how often you got them to give you that information. Then, if you get that information, claim some reason why you can't sit next to that person, and see what happens. Please report back with your findings.
I would venture to guess that if there is any truth to the story reported, the female passenger was probably asked if she would be willing to move, and probably agreed (though wasn't happy about it inside her). The other alternative might have been that she might have been involuntarily assigned an equivalent (as in same position, but in a better row) or
even much better seat, so the gate agent felt that everyone could be made happy without any sacrifice.