I had a debate with a guy on a message board about this very topic. I fell into a logical fallacy thinking that you can equate children and animals on the same terms when you really can't. The people who desire animals, simply desire animals. Its the nature of their 'condition', it doesn't make them pedophiles. You can leave them alone with kids but you may think twice about leaving them alone with Rover. (ick!)
Also, there is a difference between zoophilia and bestiality which I won't get into on this board for the sake of decorum but its something that punched holes in my theory about animal cruelty and bestiality. Its something I wish I could unlearn.