Its kinda like tire pressure systems imo, if everyone had a shred of common sense then there would be no real need for them, but people are morons. And moron stereotypically fat American exhibit "A" cant turn his/her fat ass head around to look behind as he/she backs up, and lets be honest for backing up the rear-view is just insufficient when doing something more technical. Exhibit "B" is the soccer mom who couldnt drive a pedal car on a good day, if this keeps her from backing into a car in the parking lot in her monstrosity of a SUV then job well done imo.
So do we really need it... no not at all... does it really matter though, no not really. I bet people caused the same fuss when the tire pressure systems were made mandatory, and i'll tell you what, those systems cost much more than a rear view camera would. But again I bet there will be so many loop holes none of this will matter. Do you really think the next 911 GT3 RS, or Ferrari F70 is going to have a screen for a rear view camera?