I hadn't previous heard any debate about aero vs non-aero helmets, but I do remember one other previous helmet design that did turn out to be dangerous.

Do you guys remember the brief fad of no-shell helmets? It was a reaction to big heavy hard shell helmets. Someone figured that mostly what you were protecting against was impact, so the shell was just extra weight and most of the manufacturers started selling helmets that were just the foam inner liner. *Until* it was found that the foam with no coating had a tendency to stick to the pavement, even if just for an instant, and had the nasty consequence of possibly snapping your neck The helmets could be made safer with the addition of a lycra cover, but they were phased out very quickly for the thin shelled helmets that most of us use today.