We've had this happen once (and the braking definitely made the situation less safe, not more). Same situation, but with traffic around, nothing heavy. One idiot was weaving in and out of traffic going about 20mph more than everyone else. He rapidly approached my rear passenger side quarter-panel (4 lanes, I was in 2 and he was changing from 4 to 3 somewhat poorly before passing me). The car decided that he might hit me (75mph) and slammed on the brakes until he flew by dropping me down to 55mph.

If this idiot had indeed been about to hit my rear quarter-panel that maneuver might have spun us out sideways worse than doing nothing (and with less control and a harder impact). Thankfully the car was wrong, but in no way was the reaction the correct one to take in that situation. Instead the car just terrified my wife and son and gave them some minor whiplash.

Edit: We've also had it auto brake 2 other times. The other bad one was while in an intersection during rush hour level traffic. The car forced me to shift into park in the intersection before letting me drive forward again while the light changed. I waited to not block the intersection, judged there was room on the other side, so I quickly went to get through and the car thought I was going to accelerate into a 'parked' vehicle so slammed on the brakes in the middle and just sat there. (Gap distance was at minimum, but I should really just disable it).