all I can say is..... ur crazy
So what ur asserting is, if a 4 Wheeler with fiber kit hits a pedestrian, he'll just get a push and then again he'll start to walk...!!!
but a steel bumper would kill him that instant.
With all due respect...any vehicle can extremely injure a person if its hit even at 20mph, balkeh ur correct, we should start to use the cars of early bed rock(flinstones) shayad phir sab safe rahein 
PEOPLE OF CURRENT AGE STOP USING CARS, ITS DANGEROUS FOR PADESTRIANS...Wazarat-e-Sehet 