port scanning is fine and should not be illegal. It's just "looking" at a house to see if there is a door and what type of key (protocol) it uses. Trying to open a connection on the other hand it's like trying to open the door. That should be considered as a violation.
I'd strengthen pfundstein's claim; port scanning intrinsically works by trying to open connections. That isn't enough "like" any particular physical thing to make it a correct analogy; it isn't knocking, or walking in, or opening, or anything else. But one thing we can say, without using analogies, is that it is definitely an active effort, an action deliberately taken, not something passive like "looking" is in the real world. That is not on its own proof that it is wrong... I am merely saying, it is certainly active, not passive.