what about the argument that someone could have used my unsecured wireless network to download copyrighted material with my IP address without my knowledge?
While most people protect their wireless, I know many mom and pops who still have no clue how to do any of that stuff and could be victims of their neighbor's crimes.
That would maybe work for a clueless old lady. The standard for someone with a technical background, of whom can be expected that he should know about these issues, would be higher than for someone who can make a reasonable case of not knowing about these things. At some point it becomes an "assumed liability" (that's probably not the proper term in common law systems) - what I mean is a liability for something not arising from doing or not doing something (like punching someone in the face - that's something you actively do), but rather from being in a certain position, like when you own a house, and a roof tile falls off on someone's head, you're still liable because it's your house (again this is technically not correct in tort-based systems but the principle holds). In the same way one could argue, in my opinion reasonably, that owning & using certain equipment (wireless routers) brings with it a certain responsibility, in this case making a reasonable effort to make sure that the equipment is not used to violate other people's rights. It will depend on the circumstances if this is acceptable.
In that case, Bruce Schneier is a genius... By publicizing his open wireless network, he has an excuse to download whatever he wants. And if the prosecution wants to argue for "assumed liability", what expert witness is going to trump Bruce Schneier? :)
Your assertion doesn't follow from the article. Like the other commenter remarked, Schneier is merely saying that because of the large amount of open wireless netwokrs, the chances that he's the one that'll be caught are so small that the risk outweighs the benefits.
Secondly, Schneier (as knowledgeable about crypto and security in general as he is) is in no position to be an expert witness on the interpretation of legal concepts like whether or not this liability exists in the present case. Even worse, by publicizing this article, he is basically making it public that he knows about the dangers yet deliberately ignores it, and thus enables eventual wrongdoers. I think he should talk his lawyer friends again that he mentions in the article to assess the potential extra damage he's doing to himself by publishing this. In effect it's what I mentioned in another comment above about people who are technically adept and therefore will be held to a higher standard. He's handing the (hypothetical) opposition their argument on a silver platter.
While most people protect their wireless, I know many mom and pops who still have no clue how to do any of that stuff and could be victims of their neighbor's crimes.