How can a horse respond well to a whip? It is used to promote a reaction. If a person prods a horse in the neck that is annoying to the horse the horse will move backwards. So if the whip causes the horse to move forward after the first use of the whip, how will the horse continue to react if use of the whip only provokes more pain?
There are some misconception about the use of whips. I've been working in the horse industry for about 10 years (not the racing industry, I ride and train English), and riding for over 15yr, but we use the whip nonetheless. The whips are not made to hurt, in fact, in lessons we teach our students how to properly use a whip by using it on their hand, it doesn't hurt one bit, but does make a loud noise. Most often than not, in races, the whips are waved around, not actually used to hit the horse. It is used as a signal to the horse, not as a punishment. I myself have never used a whip to make a horse go faster, but a whip can be great to teach cues, or help a horse understand what you mean (for example, when teaching a horse a side pass, meaning going side ways, you use your legs, but new horses won't necessarily understand that. A dressage whip can be carried as an extension to the leg, no need to "hit" the horse, but tapping can be used as a cue). Another example is over jump, I've had to hit my horse behind the leg to ensure a good take off. This can actually prevent injuries, as a bad take off to a jump can result in a bad fall. I'm not saying whips on the racetrack should be used, but all I'm saying is that whips are not necessarily evil. In the wrong hands, yes they are. But if used as a tool, they hurt no more than a ruler used to measure stuff. It's only when the ruler is used to punish children that it becomes evil.
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@brinkster130 said, there's lots of stuff wrong with the racing industry, whips are not a big concern. I have never in my life witness a horse got hurt from a whip. Only "bull type" whips actually hurt, the "English whip" carried during races are not meant to hurt a horse. I'd be more worried about other conditions on the race track.
That being said, it is also important to note that not everyone in the racing industry is like that, and many horses are better taken cared of than many "pet" horses. I had the chance to meet many, many racing people, and some of the horses were loved and extremely well taken cared of. I even had the chance to ride a race horse once, which was one of the best experience of my life, and those horses were just so happy to get out there. Sadly this isn't true of all race people, and there's a lot of abuse in the industry, but this is certainly not limited to the racing industry. There's likely more abuse from backward breeders (the puppy mill of the horse industry) than there is of the racing industry.
Again, I don't agree with a lot of the stuff they do, but as a horse lover that has seen the industry first hand, not all of it is evil. Some of these horses do love their job, some of these horses are well taken cared of. Just as some of these horses are drugged and over exercised. Where I am from (North Ontario), racing actually doesn't exist anymore. A decision I much agree with if it means more horses are safe and sound. Sadly, I'm not sure this is what it means, as the amount of rescue and auction horses have climbed up really quickly in the pass years (many of which end up at the meat buyer). We need to examine the industry as a whole, not just at the racing industry. Abuse, sadly, occurs much too often around horses (my own horse was bought from the auction, while being pregnant at a young age, after likely being abused).
(Sorry for the long post)