I cycle at least 60 miles per week from and to my children's schools (I drive them to school in the morning, but cycle home). I always wear a helmet, and when my children cycle with me, I require that they wear helmets too.
I have been cycling for 22 years. In that time, I have only had one serious fall from my bike, about 14 years ago. I wasn't wearing a helmet that day, and I landed on the back of my head, ended up in hospital and was concussed for days. I would not like to go through that again!