>eating pigs and cows is okay, eating horses is not
This is the situation in the UK. Some people trace it back to chivalry, where horses were very expensive and mostly owned by the nobility. But I don't know if that is the real reason.
Although it turned out that British people have been eating plenty of horse. They just didn't know it:
I think it is because of the popularity of riding, people are used to seeing horses in that role. Not quite pets, but in a relationship to people closer to that of dogs and cats than that of farm animals.
People ride horses in France, so I'm not sure that is it.