Here is a little series on my mind about what is wrong with karate. At the core, it is because the training is not literal, and most people don't get things that aren't literal. When things are open to interpretation, by definition there is more room for misinterpretation.
The Corkscrew Punch
Known in Japanese as chokuzuki or junzuki, this punch is capable of developing a lot of power and can smash through targets with proper training. Wait... that doesn't sound so bad, does it?
The problem is not the power.
One of the main problems with chokuzuki is the delivery:
Chambered at the hip or the ribcage, the arm is not in a position to defend the body or head.
The punch only develops slightly more power than a good boxing punch.
Because of the chamber position, the punch is a bit slower than a good boxing punch.
Chokuzuki was designed by Okinawan peasants to be used against a samurai, wearing bamboo armor. The focus of the punch was to smash through the armor to cause damage. An assailant wearing 80 pounds of armor was naturally slower-moving than one without armor, so more time could be spent generating more power without sacrificing defense.
Against modern attackers, who usually wear no armor, the advantage is lost.
So, you have people training to punch in a manner that will get them hurt in an attempted delivery. And usually, they don't even know the difference because the instructor doesn't know the difference. And even instructors that know the difference don't usually spell it out like it is above. So people go on their merry way, thinking that what they know can save them without ever having tried it out.
The problem is the application.
Try things out in sparring. See what works, and what doesn't. If you feel your move is "too dangerous" to use in sparring, wear protective equipment and train at half or quarter power.
Once, I was teaching a jiu-jitsu class to several brand new students. One of them was a guy who had a black belt in Shotokan karate. So when we would practice punch evasion and defenses, everyone else in class would imitate me, and perform regular boxing or streetfight style punches. This one guy was insistent upon getting into a proper stance, zenkutsu-dachi, and standing there with a motionless chokuzuki for his partner to work with.
It looked funny, because he was the only one. And because it was clearly not an effective position nor an effective technique. But the jiu-jitsu defense still worked beautifully.
Lord help us if somebody actually tries to defend himself / herself using a corkscrew punch and gets knocked out in the process because the technique just isn't designed for modern self defense.
I was taught that there were two applications: training (done exactly as before), and practical application (which looks more like a boxer's punch). Not many other schools seem to teach this way.