I think you can own ideas, at least your own ideas. Perhaps the owning of another persons(s) idea(s) isn't possible, but if that is the case then it doesn't follow that one could own an idea, even his own, in the first place: what does ownership even mean if the ability to transfer ownership, by whatever means, is absent?
Regardless, the problem is that it isn't especially clear why an idea isn't able to be owned. Specifically, if an idea is a product of thought, and thought is a product of mind, and mind the possession of host, why isn't the host entitled to ownership of his own property? If an(y) idea is produced ONLY thtough the labor of the mind of the host how can universally denying the claim of the hosts ownership of their own idea (which is to say their Thoughts) be equated with either liberty or freedom? Rather it would seem that such a notion is the height of coercion.
Once you share an idea with someone else, either through speech or action, you have no control over how others use that idea without trespassing against their real property rights.
Suppose I own a CNC machine. If I see an object, and think i can reproduce it or even improve upon it, the new idea is mine and the machine is mine. The "law" says it is "illegal" for me to use my own machine to violate someone else's "intellectual property," but this is a real infringement of my real rights to real property. Once I make my object, the idea is open to anyone else doing the same with my idea, because it is no longer something I can own when it is open to the world.
Does this help clarify the idea I am trying to express? the same idea applies to music - I can own the idea of a song, but once I record and release it, others have the right to use their own computers, instruments, voices, etc, to reproduce and improve it regardless of my wishes, because I do not have authority over them or their property. Software code, literature, etc. are similar too.
You can only own an idea you never share. Once an idea is in someone else's mind, it is beyond your sphere of control.