I wouldn't object to eating horse meat in North America, except for a few reasons:
1.) Most of these horses are retired or unwanted riding animals, which have worked hard and deserve a decent retirement, or at least humane euthanasia.
2.) Because horses are not raised as meat animals, they are treated with many veterinary drugs that are unsafe for human consumption. People wanting to get rid of unwanted horses can lie or forge documents saying that the horse has not been given any of these drugs, but horse meat intended for the butchers has been tested and found to contain these drugs.
3.) The slaughter methods and facilities used are generally intended for cattle, and are not suitable for the slaughter of horses. This results in horses being improperly stunned/desensitised and slaughtered inhumanely.
4.) Transport of meat horses is demonstrably inhumane, with former pets, riding animals, and feral animals being crammed together on small trucks. Unlike cattle or sheep, horses do not tolerate these conditions well, and will often begin to fight or lash out in terror. This results in animals with hideous injuries coming off these trucks, and in some cases horses being trampled to death in transit.
5.) These same trucks and rail cars are also generally intended for cattle, which are shorter than horses. This results in the horses having to keep their heads at an unnatural angle for a prolonged length of time, and also injuring their heads against the ceiling when the truck jolts. Horses are also frequently transported long distances with no water, food, or relief from hot/cold temperatures.
If these issues were resolved, I'd have no problem with horse slaughter/meat consumption. As it is, however, I'm firmly against it.