If the analogy is somewhat askew, but still suitable, just beginning it with "A _crude_ analogy would be ... " should amend that.
Either way, I do not believe that the faults in analogy would be any real disadvantage in a debate. Here's why:
• Old Grandpa would not be tech-savvy enough to notice the flaw at all, but he would still understand the intended message of the analogy
• The knowledgeable people that support you would understand what you really mean, and either way would have no interest in pointing out flaws in your arguments
• The knowledgeable people that oppose you (e.g Hollywood) would not want to point out the flaw for anything in the world, because then they would have to concede that piracy is not theft (a notion they are working very hard on establishing).
But if you want a more fitting analogy, how about something were people plan illegal activities in the store, instead of shoplifting? The police finds out that some customers have been discussing smuggling in a toystore that you own - the whole store gets shut down without anyone contacting you first.