I don't have time to read the article right now unfortunately, so my opinion on this might not be relevant.
Isn't it really just about indicating property? If I fenced in some land but left the gate open for people to wander in, I wouldn't mind people coming in. If I fenced in some land but left the gate shut, I wouldn't want people to climb over the fence.
The problem issues are when there's no fence, or when the gate is left open accidently. I might leave the gate open, but that doesn't mean I want people entering. If it's clear that it's my property and people aren't invited, they should be considered trespassing - unless they have a valid reason, like to knock on my door. Even then, I wouldn't want people coming to knock on my door if I'd made it clear to them in the past that they shouldn't.
Without a fence, it should still be considered trespassing if it's clearly signposted that people shouldn't be there, but I think I'd only have myself to blame if people ignored the signs and I hadn't made a reasonable effort to stop them.
In summary, I think trespassing and property rights is defined by the stated intention of the property owner. If there's a notice somewhere stating that you shouldn't be there, or if it's obvious (through security measures) that you're not wanted, then you're trespassing.
I'm still not sure how this relates to port scans, except it probably reflects differences between internet society and real-world society.
If it cost people significant money and resources every time a door-to-door sales representative walked up your front path, society would not be as tolerant of door-to-door salespeople. Most likely there would be special bylaws and rules associated with visiting people in an unsolicited way.
Things like spam and port scans are significant problems on the internet when they're mis-used, because they cost other people significant money and resources without any gain. I don't see why it should be unusual to expect similar rules or bylaws developing on the net. Exactly what they should look like would be difficult to figure out, though. ie. You could argue that it's impossible to know for certain that someone doesn't want to read your unsolicited spam until you ask them...
jesterzog Fight the light