Why isn't copying the work of someone else against their will not a form of aggression, whereas a threat (which is also just information) while pointing a gun peacefully at you IS a form of aggression?
It's coercion.
That's not true. The atoms in your body has probably been claimed hundreds of times by other people, not to mention your parents. They produced you and fed you. Why don't they own you and can sell you as a slave if they like?
When people die their are atoms abandoned and become unowned. As soon as my body goes from a lump of matter to "me", I am in possession of my body. My parents are still latecomers, even if late means only a split second later.
Here you are explicitly denying the existence of information
No, I'm not. I'm denying that it's a form of property.
Why?
Information isn't property because it isn't scare or rivalrous. If you have a car and I take that car from you then I've deprived you that car. If I make an exact copy of that car then you can still drive the car. The only reason why we have property rights is because when disputes arise and we need some objective way of deciding who owns what. If anyone could have as much of anything they wanted, a mansion, a yacht, a space ship, a house on mars, whatever, it wouldn't make any sense to have property rights. I could never deprive you of those things because they are unlimited.
If you write in a book you own, you still own the book and the writings, the physical copy itself, not the information contained therein.
Why not?
See above. Anyways, I've successfully shown that mixing your labor with something doesn't make it yours. If you steal my marble and make a statue, you don't own the statue. You owe me for damages to my marble. If you disagree then you can give me a counterexample where mixing your labor with something thereby makes it yours but simply claiming it as yours won't do. Of course, trying to offer a novel you wrote as an example would only beg the question since that's the issue we're arguing over.