I think

1. Most people are actually mostly reasonable most of the time because they don't want to die or be seriously injured
2. Generally then, your scenario is unrealistic
3. If it were true, that most people were just dying to get brain damage in car accidents we could probably deal with it in a non-authoritarian way

Consider the billions per month alcohol and tobacco cost public health systems. We still let people do these things. Frankly I'd very much be in favor of taxing smokers more if they wanted to use the public health system.

The reality is, you just like a more controlling society as I like a more free one.