If a high beam headlight could really cause harmful interference with the vision of approaching car drivers, they would not be allowed at all. Right?

Here's a sampling of interference events: http://asrs.arc.nasa.gov/docs/rpsts/ped.pdf (edit: only some of them are about EMI interference)

Instruments acting up won't automatically cause a crash. But they may contribute to the accident (ref AF447)

http://www.cvel.clemson.edu/pdf/nasa-rp1374.pdf - some examples of what lack of EMI shielding can do.