I practiced karate for years, and I still would if I hadn't moved far away. My teacher was a fan of exchanges with other schools, which is how we ended up visiting a Jujitsu school to learn some grappling moves. The instructor was a police officer that worked at the local prison.
During our first break, the instructor excitedly told my teacher that he recently found a second-hand book with techniques that his Jujitsu line had banned years ago for being too brutal. He was starting to bring them back. Later on that day he showed us such a technique that could, in theory, paralyze a man for life. He seemed very proud of that one, and was looking forward to try some of his new knowledge in his next prison riot (his words, not mine).
I shudder to think of the type of BS macho mentality that one would get from training under this guy for years - I've met plenty of karate instructors from all over the world, and they were all great teachers and great human beings. Given that I personally know of three people who had to use their karate skills for self defense (two robberies and one home invasion at night), that seems to me good enough: you learn how to defend yourself in a realistic situation, but also respect, self-improvement, and a healthy general distaste for violence.
Every time someone suggests that karate doesn't work because it wouldn't be as effective in a modern war zone, I remember that guy.