Let it be said, first and foremost, that the aim of this martial art is not to crush and destroy all opponents. Although it is indeed possible in Karate to kill an adversairy in a single blow, the ultimate goal of all budo is just the opposite: to achive inner-peace, and to avoid harming anyone or anything. Only after all avenues have been exausted, and there is no escape; only then must a karateka use the deadly skills he has aquired. For he knows that within his hands lies a means of causing life or death...
True mastery of Karate-Do means true mastery of one's self. As Master Funakoshi said, Karate, if properly practiced, can be of great benefit to society. It polishes the spirit, clears the mind, and strengthens the body. However, in the wrong hands, Karate may become evil, a tool of destruction to the society and to the user himself.
With this great art comes great responsability. Again, as Master Funakoshi said, when a karateka gains skill, he must be more and more carefull with his speach. For, in the great majority of cases, it is the tongue that is responsible for instigating a fight. It is not fitting for a karateka that he should become arogant based upon the small amount of knowledge he has aquired. A small amount of knowledge can be a very dangerous thing.
My sensei once advised me: "You must be ready at all times. Not just in the fight. So keep your mind alert at all times." A karateka should always have a clear mind. Ready to react at all times. The dullness of poeple's minds causes them to stop thinking, and to stop reflecting on life as a whole.
There are all kinds of people who train in Karate. Some do it to keep their body fit. Some do it for sport. Some do it to keep their mind healthy. All these goals are honorable, and the practitionner of Karate will receive from his training that which he puts into it.
NOTE: The generic "he" was used without any intent of discrimination. In all context, the "he" actually means he and she.