I just watched the Mitsubishi commercial of the distracted lady putting on lipstick while driving and the car broke for her before rear-ending the car in front of her. In that scenario if I'm in front of her I'm thankful her car stopped before ruining my car and my day. What a relief!
I drive a lot and I've encountered way too many distracted drivers. These safety devices are more for bad drivers than good drivers in my opinion. However, there's been a few times when traffic stopped very quickly right in front of me and i had to stop/react just as quickly without rear-ending the car in front of me. I attribute that to my "good" driving skills but in those specific situations i wouldn't mind the "extra eyes" helping me out when I've been distracted. One example, when i see an attractive woman walking on the sidewalk and i naturally want to check her out i unintentionally take my eyes off the road.
I for one welcome these driver assistance devices especially on daily driven ordinary vehicles. Sports, performance and exotic cars maybe not as much but even they would benefit in some cases. Humans make a lot of mistakes and having the aid when necessary can be life saving. But i do think you should be able to manually switch them off, with the exception being that when you power OFF and ON the car they turn back ON by default.