You're welcome to try that argument in court; if you're truly innocent it should work. The alternative sounds like a "get out of jail free" card for copyright infringement (or any other Internet-based crime).
I don't understand your "get out of jail free" comment.
It's the equivalent of being charged for robbery if someone saw your license plate number on the getaway car. While it seems plausible you could get a search warrant on that basis, unless they have other evidence I don't see how a mere IP possibly could be "beyond reasonable doubt".
Not that I'm a lawyer but I believe this will be tried in civil court where the standard of proof is lower than "beyond a reasonable doubt".
Just in case anyone is wondering, you need a "preponderance of evidence" in order to win a civil suit.