I'm unfamiliar with MIT's guest setup, but I assume they let you get an IP address, but before you can access anything, you have to acknowledge their terms of service / acceptable use policy. If you fail to abide by this, you'd be accessing the network without permission.

You're right that (as alleged), this would be an obvious attempt to circumvent access controls.

Given the way things are worded, I'm guessing that the MIT computer that was improperly accessed was a router or switch. Hell, just plugging into the switch directly could be construed as unapproved access to a computer device. I think the Federal law treats anything with a processor a computer.

Yeah, I think it's a bad argument to personify network protocols or imbue them with intent. Legally speaking, what is more important is the intent of the person using them.

There's an element of permission inherent in a door! I mean, it's a breach in a wall, specifically put there at great additional expense, just to allow people entry! In either case, an enabling technology isn't inherently an invitation. Again, just because you CAN use a technology to do something, doesn't mean you MAY.

And with respect to the comment about "this way please", and the "actively configuring my device", please note that the client initiates the DHCP conversation with a Discovery message.

  Discovery: "Can anyone give me DC info so I can set up my H, please?", 
  Offer: "Yes, I can, here's one configuration option!"
  Request: "Yes please, that sounds good, I'll take it"
  Ack: "Okay, you got it".

Note that the DHCP Discovery

Do you have any basis for claiming that "an open door could likely be construed as implied consent"?

I would not advise that you try that in many parts of the US. You'll be risking getting shot, and the homeowner would not have committed a crime.