There are so many wrongs in your argument that I have no option but to fall back to the internet pedant's way of arguing, which is to respond point by point, for which my apologies.

"If you copy my stuff, you benefit and I am unaffected. <etc>"

If something is property or not, is irrelevant to what happens when it is copied. What makes something property are the natural rights of the creator, in short - that ownership is justified through the labor of the body, over which the individual has ownership by axiom and the fruits of which are also the property of that individual.

"Property is moral because it gives a group/community as a whole a good way of managing things."

No it is not, these 'greater good' theories are nonsense. Rights exist independent of their social context. Morality isn't just a tool to organize society, it exists irrespective of how people 'feel' about it or even whether there are people at all.

"Locke understood this, which is why, when we look at the source of this argument, we find he clearly included the condition of "at least where there is enough, and as good, left in common for others"."

Right, and this is where intellectual property is even 'more' or 'easier' to see as property than 'physical' property. One man's idea does not preclude another from making his own; there is no scarcity of ideas or expressions. So there is no reason to not make an expression the exclusive property of the author; nobody else is limited in their freedoms because if the original creator would not have made the expression, it wouldn't have existed in the first place. I don't see how you're supporting your argument with this part.

"Well, IP imposes a direct physical restriction on others' personal freedom: telling someone they cannot copy something is telling them they cannot do as they please with themselves and their own property "

Yes this is faulty reasoning that I've had to put to bed several times here on HN, but I can't find my previous posts so I'll repeat. Freedom to do something only goes so far as long as that something doesn't infringe on someone else's freedom; of course my right to not be tortured infringes on your freedom to torture me. In other words, one freedom is always the other side of the coin of the prohibition of someone else to infringe on that freedom. I don't see how you can reasonably argue that freedom doesn't exist, because its very nature is that it is a protection against someone else's actions (those that infringe on the freedom being protected).

Besides, in your specific example it's not even telling others what they can do with their property; it's telling others (or rather, putting conditions on that that person can then choose to accept or reject) what to do with your property.

"The only reasonable argument for IP is the orthodox economic one of supporting and sustaining a market."

No it is not, and that's my whole point. For someone to own the expression of his or her ideas is perfectly reasonable and broadly accepted; and not (only) for utilitarian reasons, but also for fundamental moral ownership reasons. Which is why so many people feel wronged when a picture they took is used by someone else without attribution - a very common pattern, judging from the amount of blog posts about it.

Expressions of ideas represent the work of a creator just as much as a vase made by a pottery maker represents the work of that maker, and just like that maker is entitled to the ownership of the result of his labor, and any potential economic benefit he can gain from it, so are the creators and expressors (I think I'm just making up that word) of ideas. It's not because there are no practical ways of enforcing that ownership that the moral fundamentals change.