The bad rap comes from the fact that people who do not know what they are doing are given a self locking device by someone who could not be bothered to teach the belayer what to do correctly...
I have seen this in gyms literally hundreds of times...a girl who has never belayed before is clipped to the self locking device by her boyfriend (this is an example & not a gender attack or an attack on gyms) & told to just pull the rope through, then as previously mentioned when he gets to the top he tells her to just pull the handle....

& down he falls.
The point is that with an ATC this guy knows from the word go that he is not safe if she has not been taught to belay...he may be that dense that he hopes she will figure it out...but really he knows the whole time that she is clueless...most likely also the belayer won't let them leave the ground.
In the case of a self locking device however they may think its perfectly ok to not know what they are doing...
To me this is why a beginner should never be handed a self locking device & as Nic has kindly spelt out - once they have mastered normal belay they can go on to a self locking device. Don't kid yourself though...people can screw up using a self locker even if they do know how to use an ATC...this happens more than most people are willing to admit..hence the need for care
It almost always boils down to your training & care of use...many accidents in the climbing world are linked directly to carelessness and a care less attitude
Sorry about the essay but Nic's right, these devices need to be used with care & an ATC is a lot simpler to start with - it either works or it doesn't
