More applicably, imagine there is no door, not even hinges where a door should be; just an opening to the basement.

But you get arrested for walking down there anyway. Then the police tell you you're under arrest because "The owner didn't intend for you to go there."

If you wander in shouting "Lol guys, we totally shouldn't be allowed in here! Their security is awful! Quick, take pictures of all their documents and we'll post them to a news site" then you've got a more reasonable analogy.

well, all these analogies are interesting, but hackers don't get there by accident. They don't just spot the door, because these doors are invisible to regular visitor, right? You have to actively look for "doors", which implies that you have a premeditated intent of finding the "secret doors". And you also know very well that owner didn't want you in there...

Both of your scenarios are inapplicable because physically entering a property is totally unlike communicating with a public machine in the way it was intended to be communicated with.