[Sloth]

Cars can be made light and strong. You just need to work at it.

It's not just a matter of being strong. One of the things that kills people is rapid acceleration. When a heavy object strikes a light object, the light object experiences much more acceleration. That's an unavoidable fact of Newtonian physics.

[BillM]

That is pure Newtonian physics. It assumes 2 perfectly elastic objects.

The whole secret is in the energy absorbing crush zones and their physics.

A good example of this is the Kevlar Vest and reactive armor that is now being used.

[CertainInalienableRights]

It's not just a matter of being strong. One of the things that kills people is rapid acceleration. When a heavy object strikes a light object, the light object experiences much more acceleration. That's an unavoidable fact of Newtonian physics.

I agree with what you said, and it is technically accurate, but it might be more clear to say "deceleration" rather than "acceleration".

Just a suggestion. Its all relative.