well i guess its technically rape, init. whether the animal enjoys it or not you don't KNOW if they do, because we have no 100% accurate way of interpreting their communication with us. so pretty much illicit.
on the other hand, it...gives people an outlet if they want to do it, i guess. if you have something like that and its legal, then in a way it prevents people getting into messy situations by doing it illegally. i'm assuming there's some kind of controlled conditions at these places, e.g testing the animals for potential diseases etc.