The player most likely to run into the goal is the keeper. My daughter is an aggressive keeper, and did bang her head on the post once. She was diving and slid into the post. She suffered a severe concussion last year from a kick to the head while smothering a ball. She will wear headgear this week when the the high school season begins to minimize the risk of another concussion. Some protection is better than no protection.
I agree, though, that headgear should not be mandatory. Each parent should be free to choose for his/her own child. I am glad that headgear is available, and we will test it out and decide for ourselves.
A couple more seasons she should be ready to pass on the family genes.