http://www.learnliberty.org/videos/do-we-need-government/?utm_source=twitter&utm_medium=social&utm_content=Do%20we%20need%20the%20government%20to%20provide%20law%20enforcement?&utm_campaign=social%20referrals%2013
On their Twitter, posted as "Do we need government to provide law enforcement? Better yet - do we need it at all?"
Ed Stringham is the man.
Nah, he wasn't really good when it came to answering the questions of the liberal girl at the back.
I think there are better economists when it comes to this, I personally like David Friedman's approach:
http://www.youtube.com/watch?v=jTYkdEU_B4o