Roderick Long's short and sweet argument against intellectual property  begins:
Suppose I compose a poem and recite it to you. As a result, you learn the poem by heart. In effect, there is now a copy of the poem stored in your brain.
Who owns that copy?
My answer is that that if you've transmitted your poem to me without precondition, then I am morally free to do as I please with it. If you electronically wired funds to my bank account without precondition, you could not legitimately claim I owed you money if I spent the funds.
But suppose I compose a poem and offer to recite it to you for $10 on the condition that you not reveal the poem to anyone else. Clearly, I have a right to do whatever I like with the poem. Do you have a right to the poem on any terms other than those upon which I am willing to offer it?
You are certainly free to decline my terms and do without the poem. But let's say that knowing my terms, you pay me the $10 and I recite the poem to you. Are you now morally free to do whatever you like with the poem, or are you morally bound to comply with the terms upon which I offered it? Suppose you now breach the agreement by making the poem freely available to others. Have you done me any damage? Clearly, I sold you something that an individual might value; we know this because you paid for it. You have now substantially deprived me of the opportunity to sell the same thing to others, an opportunity for which I contracted with you to secure.
You now have a copy of the poem stored in your brain. Long writes:
You own yourself; you own your brain and the contents of your brain. If I owned the copy in your brain, then I would be a part owner of your brain, which would make you a partial slave ' which is morally untenable.
The poem exists and you have a copy of it. Are you morally free to do whatever you choose with the copy of the poem you possess? No, and the fact that you have agreed not to reveal the poem to others does not make you my slave.
Once I've composed the poem, I have an exclusive right to do whatever I choose with it; you cannot legitimately compel me to reveal the poem. Thus, I am free to set the terms upon which I will reveal the poem. If I wish to retain rights to the poem, I am morally free to reveal it only to those who agree to purchase limited rights to the poem. I begin with exclusive and unlimited rights to the poem, and I am free to retain those rights. I am free to contract with you to offer you only limited rights to the poem.
My rights to my mental product are primary; any other rights to it can only legitimately be derived from mine. That's a property relationship.