> all forms of propertyThe problem is that you are assuming that "intellectual property" is property. You cannot assume that.
> Enclosure of the commons was certainly for private benefit.
Enclosure of parts of the commons that are rivalrous--only one person can use that part at a time--was, yes. But as I have already said, "intellectual property" is non-rivalrous, so this argument does not apply to it.
> There are numerous aspects of physical property ownership that we just take for granted that are not at all straightforward
This is quite true; it's why we have a complex system of private property common law for physical property, and some kinds (such as real estate) have even more complexity in the law attached to them.
But "intellectual property" is not physical property, and you can't just assume that all of the law that has been developed for physical property is automatically applicable to "intellectual property" as well.
> You seem to be using a “is it for the benefit of society” test to determine whether something is an intrinsic feature of capitalism.
I am doing no such thing. Indeed, the feature of capitalism I have been describing, namely regulatory capture, is not for the benefit of society; it is a net loss to society. But it is a benefit to the capitalists who buy the regulations they want. That's why they buy them.
> That’s not regulatory capture, that is inherent to what it is.
In the sense that regulatory capture is a common end state of capitalism (where "capitalism", as I have said elsewhere in this discussion, is not the same thing as "free markets", although capitalists would love for people to think it is), yes, it is "inherent" to capitalism. That still doesn't mean it's a net benefit to society. It isn't.