Look at a motorcycle's brakes. What does the front vs rear look like?

Same reasoning for the size/power difference applies to the bicycle. I never use my rear brake on the motorcycle except when I am in a parking lot or slow moving. On a bicycle I usually use both just because of the lack of strength of the brakes, but when I need to do a panic situation, I apply full front.

Practice going at speed and doing panic stops, or slow downs using the front only. Learn where to put your body weight so you don't go flying over the handlebars. It's really not as terrifying as you are making it seem.