Size matters. Hell, even Hobbes more or less said it in Leviathan: the bigger guy usually wins, right?
Here's where you get a lot of sometimes shitty discussion around martial arts and women. "Oh, women aren't physically strong enough to take down a guy, so fighting is a bad idea." I've heard that before. "Fighting will just make a guy angrier." Heard that one too.
Bigger doesn't always win. I've seen it in my own fights and training experiences. I've seen it in traditional martial arts, mixed martial arts, and even boxing. Bigger isn't always better. Life is never simple. It's full of balance and compromises.
These two are two of the greatest full-contact karate fighters in history, and the guy on the right (Andy Hug) had every physical advantage over the guy on the left (Shokei Matsui.) But Matsui shows plenty of strength over Hug, and arguably wins the fight.
So, what's the point?
Fighting isn't just about size or strength, and anyone who tells a woman that she can't learn how to fight is full of shit. The end.
Now, does that mean I'd say that most women should fight like a man? No. But just like little men shouldn't fight big men the same way, they need to come up with strategies. At the end of the day, all people have similar weak points (or squishy points, in my own nomenclature.)
Knees, toes, groin, solar plexus, throat, eyes/face.
These all break just the same whether it's 20 pounds of force or 40 pounds of force. An eye jab will blind a guy just as easily as a woman. Smart fighting in a real life situation doesn't mean sparring, but it means using everything at your disposal to incapacitate (or kill) your opponent. A 100 pound person can ruin a 200 pound person's life by breaking their knee with a well-placed front kick. That same person can ruin another person's eye with a good hard finger jab. They just need to land their technique. And that's tricky in the heat of the moment.
This is therefore where I disagree with people who say that traditional sparring and fighting training is best replaced with specific self-defense training. You need both. Being in a situation where violence is needed and applying technique is just as much about remaining calm and collected as it is about knowing techniques. The constant din of sparring, over and over and over and over, teaches you to find calmness in violence and chaos. That calmness comes from years of experience, and needs pressure to develop. The logic of sparring is that it allows people a chance to use techniques and learn from one another while also keeping each other safe. That way, when they do need to use those techniques, they can think about what they're doing next and control the fight.
Thinking while fighting is one of the hardest things anyone can ever do. Overcoming instinct and upbringing when your body goes into autopilot is damned hard. And that's why I firmly believe that learning how to defend yourself also means learning how to control yourself. Knowing where to poke someone to incapacitate them is one thing. Knowing that you can use it when you need it is another.