Cars at least are less able to swerve unpredictably, and drivers have to complete training in order to be allowed on the road.

The standard they once met (which might have been 70 years ago) is not that good a measure of people’s driving skill today.

...and yet car-on-car accidents are still a major source of premature deaths, to mention nothing of when the cyclist is the victim. The potential to do great harm has to be the overwhelming factor when assessing road risk.

There are civil, if not criminal, penalties for suddenly swerving into another car without justification.

> There are civil, if not criminal, penalties for...

Not really, or not enough at least. Drivers can and do cause horrific accidents because of inattention, bad judgement, intoxication, and road rage. There aren't enough penalties and, it seems, the situation has been getting worse and more chaotic lately, at least where I live in the Northeastern US.

Justification is easy in the USA

This is a short list of a few common get out of jail free cards for traffic violence:

1. I couldn't see them

2. The sun was in my eyes

3. I had a medical emergency

4. The car was in my blind spot

5. They came out of nowhere

6. My car lost control

7. My brakes didn't work

We're not living in a utopis. Drivers can do whatever they can get away with. If the other party has a dashcam, then they maybe boned if the police can be motivated to do their job for once without murdering someone.