Another point that you bring up is the idea of having belt colors and stripes. Again, you are correct in the notion that people should not need that physical symbol around their waist or a rank that is assigned to them. Children, for example, need tangible awards so they can envision their goals. Stripes on a belt are excellent for short term goals, as a reward for the child for working hard and learning something. The child feels self-worth for learning.
Belts are mid-range goals, that a child works toward over time.
A test must be passed showing knowledge and skill - similar to what a regular school does. Also, note that belts have a similarity to school systems. It is a fundamental part of learning to take things in steps, where each step is a new achievement which must be recognized for the student to have a positive psychological reaction. The ultimate goal of all this belt stuff is to provide the best possible learning environment. Again, most adults don't need that positive reinforcement, but some do.