The retort would be : If you want to be able to address me, you don't have to have an open network, you can require registration and/or other physical verification first. You have chosen to run a network where you can't identify or talk to me, you should therefore know that I won't necessarily know what you're wanting. Some places have a policy that older versions of OSes aren't permitted on the network, and you'll get booted for that. Doesn't mean that you aren't welcome after you've updated your system or changed to another PC. But you haven't told me why you booted me, so I can't know for sure that I'm not welcome again.
The courts can and do, particularly when a particular crime specifies that you violate a specific placed prohibition. In Arrons case (without knowing precisely what went on), it may very well be possible to argue that he thought the banning of the mac address was e.g. a warning, an automated trip/response that the administration may not agree with in his deserving case, related to a period of overload on the system (i.e. temporary ban) etc. And the court would need to believe "beyond reasonable doubt" that none of those were the case.
The courts (usually) take a common sense approach like you suggest when your argument of "duuuhhhhhh, they didn't explicitly tell me not to do that" has very little to back it (i.e. no plausible explanation of why you thought it necessary for them to explicitly say it). But backed by a reasonable, or at least feasible, alternative, the courts often side with the defendant.
If you were able to access the network before, then you did something questionable, and now you're not able to access the network, I'd say that's a pretty good sign. At the very least, you should be able to guess why you were able to access the network again once your spoofed your MAC address. There are many layers of security on networks like these, and to be banned from an open network you have to be doing something you really know is questionable (even if you don't believe it's illegal or immoral).
The argument of "well I didn't know why you kept banning me" doesn't fly. After the first MAC filter, you should know you're no longer welcome, for whatever reason.
I like this idea, but there's a problem with it. His MAC address, which is meant to be specific to a machine, was banned. The intent is clear-- "your machine is no longer welcome on our network."
"His MAC address, which is meant to be specific to a machine"
The article (which I tend to agree with) tends to argue that a MAC address is exactly NOT that, especially in a technical sense (thus a technical user may indeed have more reason for the intent not to be "clear").
I think a better description in plain english is :
A MAC address is an address that a particular interface on a particular machine asks to be identified by in a particular session.
I.E. it's not an identity of a machine, its an identity of an interface. Its not an identity assigned by the network, its an identity offered by the machine/interface itself. Its not guaranteed to be unique, or stable beyond a session.
If it was meant to be a specific identifier for a machine, we would have many technical problems on the "legitimate" side of things, think multiple network cards and virtualised machines.
There was no agreement between Arron and MIT that arron would use a particular MAC address as an indentifier on their network. Its a downside of running an open network.
