The billboard analogy was more to accentuate the idea that he who breaks confidentiality is responsible. In the actual case of posting on a billboard Im spending money for that space. As long as Im paying the rent why would the owner take it down? He is just conducting business. He nor I are breaking the law. Unless I did in fact sign a confidentiality agreement. Then I and I alone am in breach of contract.
As far as encouraging the behavior... There is nothing illegal about that either. If on that same billboard I posted a sign that reads "No cops for 10 miles. GUN IT!" I am encouraging illegal and dangerous behavior but Im not breaking the law. Say I wrote and or published a book that explained how to do illegal activities I still havent broken the law. People who buy and read said book arent breaking the law despite the fact that I am "encouraging" the behavior. Example...
http://www.amazon.com/Anarchist-Cook.../dp/0962303208
One could argue that Powel indeed encourages people do make bombs and blow shit up. Even if someone did buy this book and did in fact make a bomb using the details inside and then used the bomb to kill their neighbor whos dog just wont shut the fuck up. Who is at fault here? Is it Powel for writing the book in the first place? Is it the publisher who printed the book? Or maybe its Amazon for selling it? No. The only one responsible is the guy who actually made the bomb and used it.