Choosing to ride a motorcycle rather than drive a car is choosing to accept some additional risk.
There is no doubt you are less likely to die of suffer serious injury in a crash if you are wearing a good helmet. Not wearing a helmet is a choice to accept more risk.
You would be much less likely to die of be injured if you were wearing full Kevlar racing gear like the MotoGP guys use. Not wearing it mean you're choosing to accept more risk.
I know guys who won't wear a helmet but wouldn't think of getting on their bike without full leathers.
Not everyones opinion of "acceptable risk" is the same. Just because someone doesn't share your opinion doesn't mean they are stupid.