Would your statements apply to people putting up posts across the front of their yard, or small boulders, or a very sturdy fence - could they also be culpable if someone was hurt?
I have been considering constructing a ferrocrete mailbox structure simply for the low maintenance aspects. I have no disire to harm, injure, or even ding a car. I have no desire for anything to ever hit it, I just do not want to have to rebuild it again like I have had to replace both metal and wood posts for my mailbox over the years due to rust and rot. (And the one time the neighbor kid took a crutch and mashed my metal mailbox rather effectively, but his mom bought us a new one.)
Is it more a matter of disguise, or simply a matter of immoveability? Is there a minimum distance that massive lawn ornaments have to be clear of the road, or do lawn-redecorating drivers have the legally allowable expectation to be able to nearly sideswipe the front porch without hitting anything in the yard that would be a danger to them, possibly besides obvious large trees?
These are very specific questions that should be address to your town council or zoning committee and a competent property lawyer.
Intent is always important, but more often than not, the state is concerned with what a reasonable person could foresee.