It all comes down to who has liability when some drunk kid gets injured or killed in there. When it's illegal and difficult to access, the government has no reasonable expectation to keep it safe, and has no liability.
Can it be illegal without penalties? There are a few laws that forbid the public from doing things (riding electric scooters on the sidewalk) but don't have any penalties associated with the act. Nor do the police enforce them.
Plus I doubt the city could get sued for not cementing the place shut. Is the state of Florida sued for not fencing off the ocean every time someone swims out in the Atlantic and gets caught by rip tides and dies? It's reasonable to expect every citizen to avoid abandoned buildings and enter at their own risk.
unfortunately if you drown off the coast of a public beach the state is in fact liable unless they clearly posted warnings and/or told you not to go in the water. This is why so many beaches have giant signs with warnings or even completely closed with no trespassing signs. If there is no warning and someone dies the owner/manager of the beach is responsible for the death through negligence for not placing a rip tide warning. If there is a clear warning or no trespassing sign then there is no liability because you did not head the warnings or entered illegally. http://masglp.olemiss.edu/Water%20Log/WL24/24.2rip.htm
"There are a few laws that forbid the public from doing things (riding electric scooters on the sidewalk) but don't have any penalties associated with the act. Nor do the police enforce them."
In New York City they absolutely do. I've seen lots of tickets given for regular and electric bicycles, and I've seen one delivery-guy's electric bicycle confiscated for just that.
