Animals, like minors, are incapable of consent. That is the only argument that works within the framework of the laws of our free society.
For all other activities considered "deviant" people should remember that we are a free country and therefore allowed to be as deviant as we so choose.
Quite frankly, having the government in your bedroom is about as "deviant" as it gets, so I say "no thanks!"
I would agree except that those who pay the bills make the rules. If someone wants to be a sexual deviant, I say more power to them as soon as all public funding is cut off from sexually transmitted disease research and relief.