Consent?
So, how do you know if they consent to you probing their ports? Was the access point drunk?
The problem with the consent analogy is that, if you have a totally sober person who is standing in the middle of the street with a big sign saying "I want some hot sex (free!)", I'd take that as consent. Though I might not take that offer up without a few tests at the local doctors.
Actually, thats not a bad analogy - the main reason I don't connect to most unsecured routers is that I don't want *my* traffic snooped on - if I'm using protection (VPN) and I'm not committed to another (corporate network) its my choice :)
Its not like most new routers don't come with some kind of security enabled that means you would have to chat to the administrator to get access to the fun stuff...