To get back to the Weir biso - I was trying to work out how to put my thoughts, but Thommo had it in a nutshell. The ' torture' aspect is all to do with the horse's confinement.
Many legends of the training ranks have used 'jiggers' or 'prodders' to get a specific response. You would be surprised at the great names in the list...my former boss used jiggers on the odd occasion ...there's an amusing story connected to one incident but I won't digress just yet..!
How does a human train an animal to modify its behaviour ? a horse should ALWAYS be confident, relaxed and happy to be with you, he should understand [ if handled sensibly ] that a rub around his head and ears is what he can expect if he brings his head to you. He should NEVER be handled roughly around the head. But how does one explain to a horse what is wanted outside of that? write him a letter? put him in the naughty corner ?
The best operators present the horse with options. The preferred option should always result in a pleasant experience for the horse, the not -wanted option should be less pleasant. Whether that is a firm tug on the headcollar / chifney if ignoring the leader, hand pressure becoming a dig in the ribs if moving over is required; or a stronger leg aid, or a reinforcement of the leg aid with a whip or spur - the horse has the OPTION . He can remove the stimulus he doesn't care for by responding - in this case, go forward - or ignore the request and receive a stronger command. His reward is the cessation of the stimulus.
The hammering of horses with whips raceday is an extension of that principle. The whip is applied to [ supposedly ] galvanise greater effort by the animal. But, if the horse is already doing its best, and the whip continues to be applied, what message does that give? it can't remove the annoyance by going faster, and eventually, it has to slow down...at which point the encumbrance on top sits up. That horse has now been taught to give up when hit.
To think that a professional horseman could confine a horse and repeatedly apply a stimulus that it cannot answer is torture indeed.
Nothing to do with electric fences. Any smart horse won't touch one after the first lesson, and I've seen clever ponies carefully listening for the pulse of the current and diving through to greener pastures at the right moment. No fear there, just [ again ] a conditioned response.