While I think it's important to wear a helmet, unfortunately the helmet debate will be raging on for generations to come. Some people don't like wearing one, some people flip out every time they see somebody not wearing one and start hollering up and down. Honestly the best you can do is state your piece, and then if the person refuses to listen, it is on their heads (literally and figuratively) if they become that one in a million.
Unfortunately any sport runs the risk of injury. I think that a $50 helmet is cheap insurance against what could be a lifetime of medical costs and heartbreak. But I choose this for myself- I don't have the authority to choose it for other people.
To me, the importance is WHAT you are protecting. A traumatic brain injury can mean the difference between living a normal life and being a vegetable. You can heal from a broken leg/arm, cracked ribs, a bad fall- you might have lasting effects, but typically they are not going to change how life is lived. My brain is how I make my living and survive. I insure my car, my apartment, my belongings, so insuring that my brain is protected (so far as it can be, no safety method is 100%) is important to me.