Think about this for a minute. This view would not be the view of the creator of an intellectual idea, who is interested in controlling the use of the idea he has created. He may, for example, stipulate before discussing an idea that he is only revealing his idea to parties that agree not to further pass on the idea. Thus, anyone who violates this agreement, by passing it on after agreeing not to, would be breaking a contract, that is, they would be committing an injustice. Thus, it is not hard for me to see how an injustice can be committed in the world of intellectual property---unless you don't believe in the sanctity of contracts.
But let's move on to the case of a third party, who does not have authorization from the creator to pass on some type of intellectual property, but nevertheless has obtained a copy of the property from someone else who has violated the terms upon which the creator passed on the property.
As soon as a creator contacts the third party and informs him that the property he is redistributing was issued to him via a broken contract, then, one would think, that, in a libertarian world, the third party would want to stop passing on the property, that is, unless he is a criminal.
What possible justification could a third party have at that point to continue reproducing the intellectual property, once he knows that he has obtained it via a broken contract? His only defense is to distort the range of damage that could be done to the creator.
The "you still have your copy" view is the perspective of the person who has without proper authorization obtained the creator's work and is in some way using the work in a manner objectionable to the creator. That is, the unauthorized user's reply may be, "Hey, I have a copy, but so do you." But, why is this advanced as the supposed key focus point of the creator of some intellectual property? That the creator of an intellectual property may still be able to use the property that he created may not be the key focus of the creator at all. Indeed, it might very well be that the creator's focus may be on the fact that unauthorized use of an intellectual creation may result in competition in the market against his ability to market the property and thus lowers the revenue stream that he may be able to achieve from his creation.
Indeed, personal use value may not even be of importance to a creator. If I stop blogging, the only value that my formula, on how to get linked on the Drudge Report, may be the revenue I can earn by selling the formula.
The "Hey, I have a copy, but so do you." is a distortion of what may be the value to the creator of a given piece of intellectual property. It is not the view of a creator of a piece of intellectual property, who wants to protect his creation. It is the weak justification of someone who has obtained intellectual property through a broken chain of authorized use.