Correct me if I’m wrong, but isn’t a horse’s temperament largely a product of how it was reared?
Largely, perhaps. But it’s debatable how much.
Nipping and biting is a normal behavior between horses. They must be trained to not nip and bite at people.
Poor training can increase biting and good training can reduce it. Especially if the nipping/biting behavior is related to treats or food.
Describing the species as “naturally vicious” is stupid though. That’s a designation for wild predator species, not domesticated prey species.
Domesticated horses have no natural tendency to attack, bite, or kick human beings. In general they tolerate or actually like us. They injure humans only because of the tremendous disparity in size and weight between humans and horses, and because humans often carelessly do things that are alarming to a prey animal. They have a different visual system than we do, and often get alarmed when they can’t resolve something that’s visually clear to us humans. As prey animals they react to sudden movements by prudently departing the area, or by kicking at it if it’s coming up behind them.
Usually if a horse is handled with kindness it will react with kindness, if not actual altruism. But there are differences for breeding stallions, some hormonal mares, or racehorses who are kept highly fed and allowed out of their stalls only briefly; you can get some bad behavior there. As with any species, it’s possible to unintentionally teach a horse to engage in bad, spoiled, dangerous behavior by being too unassertive.
People can be incredibly stupid in the way they allow their innocent children to interact with horses. I have seen people drive into a horse-breeding facility, pull up to a paddock, and let their children out of the car to go hug the horses before stable staff could run over and stop them. Other people will allow toddlers to walk underneath horses during fly season, when the horses are kicking at flies. Madness! Either of these incidents could have resulted in death—not because horses are vicious, but because they’re big. And of course, these are just the sort of idiots who will sue.