Why does karate exist?
Karate is more about finding your personal balance, harnessing your inner energy, and being in control of your movements than it is about fighting. It exists for people who want to achieve those things.
10 degrees of black belt exist in Karate. But each belt has a meaning. The meaning of the 10th degree is "perfection", not in those exact words. Because some people rightly believe that no one can be perfect, some Karate programs have eliminanted the 10th degree. An example of this is the ATA program, they only have 9 degrees of black belt.