Humane euthanasia, retirement/rescue organizations, finding a new home with someone local, or letting a horse live out his or her life are far preferable to slaughter. Perhaps laws to limit breeding for sport? (Not sure I support that but would like the possibility to be considered.)(And to horse racing bashers, the majority of horses headed to slaughter are not thoroughbred horses who raced. Honestly, though, I'm not sure about quarter horses.) For many there is a different kind of emotional attachment to horses; whether that's sensible or not, that's the way it is. Horses have helped humans in uniquely different ways than cattle and other animals, so to many the idea of chomping down on a slice of horse is just a disgusting slap in the face to these noble creatures. Horse slaughter had actually dropped since the '80s from a level of about 300,000 per year down to today's level, though in recent years it's risen slightly; I don't see thousands of horses roaming around unwanted since the drop in the '80s, do you? The pro-horse slaughter folks are in this for one thing: the money.
Here's a decent overview of some facts and arguments on both sides:
http://ncseonline.org/NLE/CRSreports/06Jul/RS21842.pdfAnd some thoughts from folks in the racing industry:
http://www.bloodhorse.com/articleindex/article.asp?id=33920"When you own a horse, it's your responsibility to care for that horse. We can control their conditions as human beings," said Gretchen Jackson, owner of Kentucky Derby Presented by Yum! Brands (gr. I) winner Barbaro, who is recovering from a severe injury he sustained during the Preakness (gr. I).
Arthur Hancock, who bred and/or raced three Derby winners and owns Stone Farm near Paris, Ky., concurred with Jackson and warned Thoroughbred sellers to watch out for suspicious "killer buyers," who often use misleading information to coax people into selling their horses for cheap prices, after which they are vanned straight to the slaughterhouses.
In addition, thousands of horses are stolen each year, including two racehorses that were recently unlawfully taken from a barn at Thistledown to be sold on the slaughter market.
"I'm for outlawing the slaughter of horses because they're not bred for the food chain--they're companion animals. (Slaughtering) is a betrayal of trust," Hancock said. "It's a very vicious practice and it's not necessary," he added, pointing out the retirement farms across the county that are willing to give good homes to Thoroughbreds whose owners can no longer care for them.