Welcome to the Cellar, sgr.
You're right, animal fights have been the pastime of many cultures. Common livestock in very poor cultures and specially bred fighters in wealthier ones.
Leah said they shouldn't be forced to fight but should have said they shouldn't be allowed to fight. All they need is an opportunity because it's their nature.
Boxers fight for sport and money, wild horses fight for sex. Horses are smarter.