> I could defend it by keeping it a secrete, or announce to the word that I am in fact the inventor (ownership of an idea does not necessarily have to imply exclusive use of it).

Defense of property is defense from an aggressor trying to take that property from you. The things you've noted may be defense in some general way, but they certainly aren't the sort of "self defense" that is implied when speaking of defending one's property.

In particular, defense ought to be expanded to "the legitimate use of physical force or threat of force in proportionate response to the initial use of physical force or threat of force against your person or property."

In this sense, IP absolutely requires a coercive third party.

> You're claiming that the attribute of physical exclusivity is essential to the notion of "property"; I can argue that it is incidental. The import thing is that thorough appropriating your property, I am depriving you of some tangible benefit.

You have it backwards. The only reason why you're depriving me of some tangible benefit is because it's scarce. If you take some resource from me that isn't scarce, then no benefit is lost because I can immediately conjure up another resource of identical value. Therefore, there is no conflict.

> In case of intellectual property, the benefit maybe competitive advantage (if I choose to keep my knowledge secret), or a revenue stream (if I choose to allow others to benefit from my knowledge in return for compensation), or reputation and status (in being acknowledged as the inventor).

Defining property in terms of tangible benefits is simply untenable because there is no bound to it. For example, I could claim that the person who lives next to me lowers the value of my house because they never cut their lawn. I could therefore claim that they are creating conflict because they are removing some tangible benefit that I have.

We can't define property in terms of "tangible benefits" because "tangible benefits" could be just about anything. It makes the concept of property untenable as a means to resolve conflict and this is why it is rejected.

> This obviously wrong. Reputation, influence (political religious, etc), honor, status, competitiveness -- all quality sources of "interpersonal conflict".

You're misinterpreting the piece you quoted by assuming that "interpersonal conflict" can mean any kind of grievance someone might have. Frankly, that's ridiculous and defeats the whole purpose of having a system of ethics in the first place.

Kinsella makes it quite clear that interpersonal conflict is conflict in which one person deprives another person the use of a resource. This can only happen when the resource is scarce, otherwise it cannot be deprived from anyone.

> In fact, the paper conveniently avoids tackling some forms of intellectual property--trade secretes and trademarks-- by dismissing them as "less problematic" (thus tacitly acknowledging the validity of the concept of "intellectual property")

The paper does address them, you just didn't read those parts. Trademarks are discussed starting on page 43 and it's quite clear that no validity is given to the concept of intellectual property rights. Instead, some aspects of trademark law can be enforced with respect to the consumer (via charges of fraud).

> It is thus drawing an arbitrary distinction between different forms of intellectual property

It's not. Everything is explained. You're taking the "less problematic" portion out of context. Kinsella proceeds by arguing that any law which depends on the notion that ideas can be owned is illegitimate. He then goes on to show how most laws under the umbrella of "intellectual property" depend upon the notion that ideas can be owned (and are therefore illegitimate). Notably, there are some laws that don't depend on idea ownership and therefore could be legitimate.

This isn't arbitrary at all because it's consistently applying the illegitimacy of owning ideas.

> Note that the classification of physical property is also essentially arbitrary

It's not surprising one would think this. Property isn't exactly a universal law of physical reality. It's a useful heuristic that can be used among a collection of individuals who seek to resolve conflict peacefully in lieu of violence.