The US Navy requires all occupants of helicopters to wear a helmet. They use a cloth/fiberglass model for passengers that offer head protection and hearing protection. David Clark had a similar model at one time so I suppose it was them what sold them to the Navy.
The Bears (....errrr....excuse me....the Passengers) would howl about being required to wear such a thing but if sold to them on a safety basis....they might go along with the concept then helmets for pilots would fly too.
If helmets are proven to be a safety improvement for both crash protection and hearing protection as they are....then why the resistance to wearing them?