So what's the case for not using bright lights on the road?
IIRC the argument is that you dazzle or confuse a driver and instead of driver thinking "hmm what's that?" and slowing down or displaying a bit of caution they just carry on regardless in a state of confusion/dazzlement.
I'm not sure which way I fall on this one to be honest, I don't like regularly being dazzled by car lights whenever there is an undulation in the road, but the idea (and some personal experience) that drivers might be unsure but carry on anyway sounds believable (and damned scary).
<edit> pretty sure this was the argument put to me when I was talking about aiming a bright headtorch at drivers nosing out of side streets an effort to stop them pulling out infront of me. As posters below comment there could be issues for oncoming traffic.