People eat seals, deers, snakes, rabbits, dogs, horses, cows, sheeps, worms, ants....
The difference between them is the culture and how people pet them in their mores. There's everal market of horsemeat in Spain, under the health EC follow up. It was not a country of cows but horses. Here cows and milk gastronomiy culture weren't very widspread except in very high mountain villages. Mediterranean weather doesn't allow a good conservation of lactic products. That's why olive oil was/is more common than butter in kitchens.
When the culture of petting domesticated animals was a civilization standard, some countries stop eating some sort of animals. Industry revolution mark a path in traditions.
If you're talking about the crime of using meat for animal feed, as a cheap substitute for meat in human food instead of the approved sanitary, that's another story.
Haven't seen war horse, but to me it seems to be a story about war, where one of the main protagonists is a hors, not a story about horses. Black Beauty I have seen, I think, but can't remember anything about the plot. Anyway, provocation succeeded. 
