I think the issue comes from the fog light being such close proximity to the brake light, mot regs of that time, say that a fog lamp must be mounted centrally, or O/S mounted, but I think that the introduction of third brake lights in the late 80s changed things.. as I remember, cars that had 2 fog lamps generally had them bumper mounted, or on a different light cluster from the brake light. At the end of the day, it comes down to common sense, if your already blinding someone behind you, why increase the risk of them running into you!
Tom