Size is not the same things a weight. Crumple zones are what size buys you in modern vehicle design, and you don't have to have a heavy car to have nice big cushy crumple zones.
This discussion started about size, not weight.
Maybe you have extraordinary reflexes and could have accelerated out of the way, or slammed on the brakes, but the average driver? I think not. I'd like to have some serious steel and crumple zone between me and that motorist under those circumstances, and the tiny little electric buggy is probably not going to have the same amount of protection as a large SUV.
I'd sooner be in the light car with a chassis that doesn't get crushed into the cabin than a heavy car which does.
https://www.youtube.com/watch?v=C_r5UJrxcck I know which one Id like to be in..
I was driving a Toyota Camry. If I'd been driving a large truck, I probably couldn't have avoided the crash.
When I buy a car, I want to know both how likely it is that I can avoid a crash (manueverability, stopping distance, ABS, etc) and how likely it is that I can survive one if it happens. Both are relevant.
Consumer Reports' 2016 Automotive Edition had a lot of discussion about car safety. Most of it was centered on technology that helps to prevent accidents or make them less severe. Eg, if your car detects that you're about to hit something (Forward Collision Warning) and has Automatic Emergency Braking, you might not hit it, or hit it at 30mph instead of 60mph.
That could save your life. To say that the weight of your car is a safety factor but stopping distance isn't is just silly.