if you go thru a yellow and are involved in an accident, you are automatically at fault.
Are you sure you're not accidentally mistaking it with people running a red? What if the light just turned yellow? If a light turned yellow 0.5 seconds before you entered an intersection, is it your fault if you crash? Most people can't react in 0.5s, let along bring a car to a stop.
I'm from BC, and here it's VERY different from what you've described. The yellow light means you have to stop, unless you cannot do so safely.
Authority: I crashed late on a yellow last fall, and was judged not-at-fault by the government insurance company. The cop who attended the crash scene reviewed my dashcam footage and said 100% the other guy's fault. Further authority: discussion with the bodyshop manager, who gets to see whose insurance claims are at-fault or not.
The was this situation would play out in BC if he had crashed:
1) He entered on a yellow, going straight through.
2) In BC, the car going straight through has the right of way.
2) Turning car started to turn, without ensuring that the way was clear, and that oncoming traffic was actually going to stop in time.
3) In BC, the turning car doesn't have the right of way, and has to yield to oncoming traffic.
Simple and straighrforward.
Where it gets messy is if if a car runs the red. If straight-through traffic runs the red, and the turning car proceeds, the turning car *may* still end up 100% the responsibility of the turning car. That's what the bodyshop manager tells me, anyhow. I don't know if any of those situations had dashcams, though, so it might be that the decisions tend to go this way due to he-said/she-said. Perhaps dashcams would vindicate the turner in this situation, where straight-through traffic runs a red.