You're talking about bestiality, also known as zoophilia. I personally do think it's wrong and a sickness. I think it's much like pedophilia, in that some people who engage in this behavior think they're expressing love for the object of their affections; however, there are others who simply don't care, desire sex with the person/animal, and don't care if they're hurting him/her/it.

There's a documentary called "Zoo," about a man who had sex with a horse, and the horse presumably kicked him and killed him. There are zoophiles who speak in the documentary.

Going by what I have read--and I'm not stating this as fact, because I don't know that it is--it's quite common for farmers to have sex with their animals; I'm not saying most do, but I'm not saying most don't, either. It seems a lot do, but again, I don't know what the truth of the matter is.

A long time ago, I got into an argument (others who find bestiality offensive participated in this argument) with a guy online who joined a chat group I was part of who said he had sex with his horse, and defended it and said there were many like him. Of this, I have no doubt; just as there are many pedophiles and ephebophiles, there are many zoophiles. They aren't open about who they are, so we don't see the true numbers. But they find each other and join groups. They protect each other.

I consider it animal cruelty, because, like a child, an animal can't consent. Even if the animal shows sexual arousal, it's like with a child, who can't understand the consequences of the actions, and we can't know that an animal isn't left confused or unsure. Some animals can be harmed physically, as well. I've heard of people who have sex with chickens, and the penis rips the chickens' butt holes, and they bleed to death.