I think a lot of it has to do with closing speeds. I've nearly hit pedestrians once or twice because I was doing a short sprint and they didn't expect a cyclist moving at 30 mph. They didn't realize how fast I was going until they were already in front of me.
As for light pairs, I think the relevant comparison is motorcycles with dual beam lights. The danger of two light is that other drivers might think you're a distant car, rather than a cyclist with narrow light spacing.