Your first line distinguishing people from humans is a moral perception.
It denotes an underclass that following that perception could be constituted as property.
It doesn't "denote an underclass." It denotes two separate things.
People are defined by their reason, not biology. Little green men from Mars are people, but not humans. Maybe there's a dolphin somewhere that has attained person-hood; if so, it's certainly non-human.
Think of a Venn diagram. "Person" is a set that overlaps some of humanity. It also may overlap many other creatures, if we consider the whole universe (and, given the size of the universe, the odds approach 100% that many other planets also developed reasoning life).
To say that only humans can be persons would deny the person-hood of uncounted and uncountable masses throughout the universe (and possibly here on this planet, if some apes or dolphins or computers develop enough).
Self-ownership is only a "natural state" of reasoning beings. An animal can't comprehend the concept of self, let alone own itself.This is debatable. Many animals do have a concept of self and their very survival instinct and ability to learn can be argument that they 'own self' and reason how to protect it.
Instinctive reactions are not the same as reason and self-ownership. I can build a robot that will "defend itself." That doesn't mean it actually understands selfhood, or is a moral actor.
I don't believe that it puts them on the same moral agency level as humans, just that to moral agents there should be a distinction of treatment between animals of varying intelligence.
Self-ownership is binary. You can't "kind of" own yourself. You either do, and you are a moral actor, or you don't, and you're a thing.
While I might have aesthetic
opinions on the treatment of higher animals, those are not morality, and no one else is obligated to respect my personal aesthetic notions.
In other words, if I am going to say I am a moral agent, I had better not just assume that means I can do whatever I want to anyone who I don't think is a moral agent. Rather, being a moral agent requires of me to consider the sentience and sapience of my fellow creatures and treating them according to their emotional, psychological and sensory needs, so much as it is in my ability.
No, you shouldn't just assume. But that doesn't mean you can assign "levels" to something that's an "all or nothing" proposition. You can't be a little bit pregnant, and you can't be a little bit of a moral actor. Any moral actor has all the rights of any other moral actor. Any entity that is not a moral actor has no rights whatsoever (and, in the same vein, no obligation to respect rights - a bear can kill you, but it is not "wrong" for it to do so - morality doesn't enter into its life).
As soon as a moral agent dismisses another creatures suffering as unimportant because they are 'lesser' that person ceases to be a moral agent.
Prove it. With logic, not just an attempt to impose your own biases on others.