Likewise in some high-crime jurisdictions, if you did not lock your car you are liable for it getting stolen or broken into[2]. An unlocked car is too tempting for some people to just walk past and not take it.
I know it might sound crazy but you could make the argument that a massive pool of highly-structured and very valuable data just sitting out in the open is an attractive nuisance and steps should be taken to put it behind a locked gate. Once that requirement has been satisfied, normal trespassing laws apply.
[1] https://en.wikipedia.org/wiki/Attractive_nuisance_doctrine
[2] http://www.cbc.ca/news/canada/montreal/ndg-resident-question...
For example, if a woman walks down a dark alley wearing short skirts and gets raped, it isn't her fault. I mean can you imagine if we said "well, she was just an attractive nuisance!" The judge would throw the book at you.
I am saddened by this.
The analogy is starting to break down, but I think it's still instructive for the problem of applying a simple first principles approach.