I read that you get a nontrivial discount on your car insurance in Russia if you have a dashcam. So basically everyone there has one, which is why it seems like all the dashcam videos on the internet take place in Russia.

I think that sort of system makes sense. We shouldn't require dashcam, but any policy which reduces expensive he-said-she-said litigation in our society should be encouraged.

I suspect we'd find a pleasant second-order benefit as well: humans might simply drive better if they know they're being recorded. We know that interactions with the police are much less likely to escalate to the point of violence when both parties are recording each other, and I imagine the same principle could apply to our roads.