Can anybody explain just why the left foot braking is such a bad habit? Or, is it perhaps just urban car legend?
Personally I think it's a carryover from driving manual transmissions before automatics existed. Then you used the left foot for changing gears and the right foot for braking/accelerating. As auto trannys became popular they still taught how to drive manual but if you ended up in an automatic, then all you did was drop the use of the left foot.
I don't think there's anything wrong with using the left foot for the brake as long as you do it properly. I've done it on a performance track.
In fact...if all one drove was an automatic maybe (and I just had this realization and haven't thought it completely through yet) just maybe it would eliminate the 'wrong pedal syndrome'. We've all heard the stories of someone slamming their brakes and the car sped up but after the investigation it was actually driver error when they slammed the accelerator thinking they were hitting the brakes. There was another Prious sudden accleration the other day that was deteremined to be driver error in this very manner.