A friend of mine went across the hood of a car while wearing a half helmet with a sticker on it that said “Helmet laws suck”.
After about two years of plastic surgery to put his face back together he went out and got a full face helmet. He still disagrees with helmet laws but these days he says helmet laws only protect the stupid, the smart guys are wearing helmets and don’t need to be protected.
I'm sorry he had to learn the hard way, but as another poster pointed out, one may experience a glancing blow. A helmet in such a case could mean the difference between life or death.