That's what airbags are supposed to help with, thankfully.

Yet 53,000 people a year in the US suffer traumatic brain injuries from motor vehicle crashes.

If we are to believe a helmet will help a cyclist, it must be true that helmets would have helped those drivers and passengers too.

The airbag argument is just distracting. "Let's not use antivirus because we already have a firewall".

https://www.cdc.gov/mmwr/volumes/70/wr/mm7048a3.htm#T2_down

At racetracks, they're usually mandatory. It's all a matter of risk vs. inconvenience.

I don’t think helmets would mitigate that risk. For comparison, should bicyclists be required to wear seatbelts?

Race car drivers wear helmets, so clearly they help.

Race cars are built differently; they have a tube frame to protect against high speed roll overs and have no airbags. You wear a helmet to protect yourself from hitting your head against the metal roll cage or steering wheel (because no airbag).