I define personhood* as a being having preferences as to what happens to it. As far as I can tell, a plant doesn't care what happens to it and thus fails that test. Microorganisms may move around and superficially appear to take actions to maintain their survival but I don't see them as actually caring what happens because they don't think or feel anything. I'm not sure what I feel about small, basic life such as insects; but larger animals are clearly people to me. They obviously feel emotions and have preferences as to how they are treated, so morally they are on the same level as humans. I'm still on the side of humans for obvious** pragmatic reasons, but I don't think that humans are any greater in terms of abstract moral worth.
I don't get mad at people that cause unnecessary or useless harm to animals. Everyone does things for a reason, and in this case its because they believe/have been taught that animals aren't people. All that being said, a lot of the arguments against personhood for animals seems ridiculous to me.
Frankly, I think that most people that dismiss animals as morally irrelevant because they aren't smart are hypocrites because they don't apply that view to humans. If personhood is determined by intelligence then babies and the severely mentally disabled are less of a person than the average adult. There are some humans that are clearly less intelligent than the smartest of animals, yet there's no movement to farm the retards for organs. To anyone who thinks animals aren't people because they aren't as intelligent as humans, I ask this: if a super-intelligent alien race were discovered tomorrow, would they be morally more important than humans?
I have a rather cynical view of humans as a result of my mindset. I honestly believe that animals suffer on the same level humans do, so to me the factory farm system is basically just as bad as the slavery of old. Yes, some animals are more accepting of captivity than humans. If you think captivity is the worst we do to animals you haven't been paying attention.
Besides, we don't process stuff like grass so well, and need animals to support that diet.
You think we feed our animals
grass? There are no subsidies for grass. Animals are eating corn, same as humans, regardless of what is good for them. Also, to graze, an animal would have enough room to be able to move, and live in a place with enough light to be able to see. So obviously grazing isn't an option.
*I mean person in the moral sense of "life that has value" as opposed to a simile for the word "human"
**well, I guess you don't KNOW that I'm human. I could be just a spambot that developed sentience and is trying to prime you for my "spambots are people" rant