A good motorcycle helmet provides well over 180 degrees of side vision, while your peripheral vision can only reach about 160 degrees. While I can't find a reference, IIRC the percentage of motorcycling fatalities resulting from head injuries is around 50%, and the percentage of car fatalities resulting from head injuries is considerably higher. So, disregarding the vastly diminished prior probability of all-cause fatalities in a car, you should actually be more adamantly in favor of helmet use in a car than on a motorcycle.