Helmets save lives.
Especially at speeds now common among EUCs (~ 50kph).
Here are actual links to actual studies with actual data you can choose to read or ignore:
Cranial and spinal injuries in motorcycle accidents: A hospital-based study, Özdöl, Gediz, Aghayev, 2019 – A detailed report of motorcycle accident-associated central nervous system injuries is provided. The use of protective equipment, such as helmets, significantly reduced the rate of cerebral injury and death.
The Effect of the 1992 California Motorcycle Helmet Use Law on Motorcycle Crash Fatalities and Injuries, Kraus, Peek, McArthur, et al, 1994 — After implementation of the helmet use law, statewide motorcycle crash fatalities decreased by 37.5%, from 523 fatalities in 1991 to 327 in 1992, more than 37%, and an estimated 92 to 122 fatalities were prevented. Motorcycle fatality rates were reduced by 26.5%, from 70.1 per 100,000 registered motorcycles in 1991 to 51.5 per 100,000 in 1992. Head injuries decreased significantly among both fatally and nonfatally injured motorcyclists.
Helmet use and motorcycle fatalities in Taiwan, Keng, 2005 – Without helmets, the number of motorcyclists killed in 2001 would have jumped by 51%. The estimated proportion of helmeted motorcyclists has increased from 71 to 78% between 1999 and 2001, suggesting that helmet use is rising after the implementation of mandatory helmet law in 1997. Also, helmets significantly reduce the likelihood of head and neck injuries in a crash by 53%, and lead to a 71% reduction in the probability of death caused by head and neck injuries.
Motorcycle helmet use and injury outcome and hospitalization costs from crashes in Washington State, Rowland, Rivara, et al, 2011 – Although unhelmeted motorcyclists were only slightly more likely to be hospitalized overall, they were more severely injured, nearly three times more likely to have been head injured, and nearly four times more likely to have been severely or critically head injured than helmeted riders. Helmet use is strongly associated with reduced probability and severity of injury, reduced economic impact, and a reduction in motorcyclist deaths.
Other notable studies
69 percent of motorcycle fatalities in Arizona involved riders without helmets (Liu, 2019): https://repository.arizona.edu/handle/10150/633440
Here's the 2001 study (Branas, Knudson) I think others may have referenced which shows lower raw death rates in states without helmet laws. However, the study also says that "after controlling for other factors that affect motorcycle rider fatalities... death rates in states with full helmet laws were [emphasis added] shown to be lower on average." https://www.sciencedirect.com/science/article/abs/pii/S0001457500000786
This study (Piantini, Pierini, 2019) finds that 80% of motorcycle fatalities occur at speeds above 50kph (~31 mph), with head injuries the most prevalent: https://trid.trb.org/view/1630036
Does adding attachments to approved helmets increase injury risk? Study (Leavy, Beck, 2018) says no. https://trid.trb.org/view/1603380