Ok, let's take one more run at this.
1) before the copyright violation, there is no copy.
2) A hacker makes a copy of a file that you assert rights over, without your permission, by burning that file to one of his CDs
3) You are asserting that the copy is somehow your property, but it isn't. The CD belongs to the hacker before, and it belongs to him now. He has the store receipts to prove it. Attempting to seize that CD would be theft on your part - you attempting to deprive him of a CD that is indisputably his own property.
4) The problem is that that CD has been changed so as to form of a copy of your intellectual property, which you have right over. Those rights have not been removed from you, nor have they been lost or transferred. The physical copy is not your property, never was your property and you have no legal rights whatsoever over the physical copy as an object.
5) The reason why people don't agree that copyright is theft is because theft involves the transfer of property from one person to another, and none of your property has been transferred. There is not a thing that has been stolen.
6) The fact that copyright violation is not theft tells us nothnig about either legality or the desirabiltiy of copyright violation. Murder is not theft either, but that doesn't mean anyone is advocating killing sprees.