To ignore a dangerous incident caused by a driver is, in a way, to condone it. Any way that would communicate the driver's error to the driver that would be non-hostile would be better than saying nothing. but, of course, there is always a risk involved. In all my interactions over the forty years I've been riding, I've never gotten into anything more than an argument, never escalating to the point of violence. I assume that if I were right, the incident might have some possible effects on the driver the next time he interacts with a cyclist. But, of course, there is no guarantee. But it's all a matter of one's personality and inclinations..