its rather like the smacking argument with children. A smack, as in a slap with an open hand, on a child's bottom or hand, is a completely different kettle of fish from taking off your belt and beating a child black and blue with the buckle end.
If my horse goes to run out at a SJing comp, and i give her a smack with my whip, and then she sorts herself out and jumps as she has been taught to do, there's nothing wrong with that. If I sit there, in the middle of the ring and wallop her over and over and over again before I even represent her, then that's abuse (and i ought to be eliminated, if the judges are on the ball).
If the governing bodies say that no-one is allowed to use a whip under any circumstances, then it doesnt give the judges any room for personal repsonsibility. what about the rider with a slightly dodgy right leg, who needs the whip to back it up? What about my horse who ALWAYS ducks out to the left, which can be avoided if I simply hold my whip in my left hand?
Brilliantly and succinctly put, Gruntfuttock.