I have neither pets nor houseplants. I have had pets, and yes, there's an emotional attachment there. But it's one we ascribe to them - the value is not inherent in the animal, it is ascribed by us, the human. Therefore that animal is not inherently any more valuable than the plant by dint of the fact that it can walk around and slobber. At no point am I saying "It's okay to be cruel to animals". You shouldn't be cruel to anything because it's wrong. But if keeping an elephant in a pen that does not physically harm it provides a benefit to a human - even if it is only an aesthetic one - I consider that acceptable. A pet is there to make you the owner feel good, anything more is simply fooling yourself.