There are just some people who were raised in such a way that they simply will not raise a hand against a woman (or a girl).
When I was in college, I took a Tae Kwon Do class, and the teacher insisted on co-ed sparring. It was something that I just wasn't capable of. I told the teacher that I wouldn't spar with a girl, but I'd be happy to spar with any of the guys. I was told to get on the mat with a girl, or I'd fail the class (1 credit). So, for a few weeks, I had to spar with both guys and girls.
I was very popular with the girls for sparring, as they got to use me as a human punching bag. All I'd do is cover up as best I could. I was also pretty unpopular with the guys as a sparring partner, as I got pretty grumpy being used as a punching bag by the girls.
After about 4 weeks, even though the teacher saw that I was capable of sparring with the guys and making some improvements, he refused to allow me to only spar with the girls, so I dropped the class.
Mark
I had to deal with it first when my then-16-or17yob started in Karate. He had to spar some girls, wrestle, the whole nine. He and I both had qualms about it -- more from the perspective of the "beating up on a girl" deal. Now that I too have started karate, I've had to deal with the same issue PLUS that of "beating up on kids," since the closest to my height sometimes are 12, 15 years old. (Although in all truthfulness, at this point in my development, I'm far more often the beat-ee and the beat-er!)
The way we've both made peace with it is this: one purpose of the class is to teach these girls, these kids, to defend themselves. If all they spar is girls, or guys who hold back, they will in NO way be prepared for a real-life experience. Girls and kids aren't attacked by nice men who give them a pass.
So I'd be lying to you if I said I take any satisfaction in jabbing a girl, or seeing a kid backing away from me with an alarmed look on his face. But before God, if I learn one day that ONE girl/kid was able to hold his/her own with some miserable adult attacker in some degree because I'd given him/her an opportunity, in a safe and controlled environment, to face his/her fears and learn to defend himself/herself -- I'll be a very happy man.
Dan