I don't think I buy the "you forfeit your rights to private property when you park it on the beach".

I park my car in "public" parking lots all the time. I have a "reasonable" expectation that my private property will not be tampered with even though there's no warning or proactive enforcement mechanism.

I think that you're right though - these days you have to basically expect that your property will be vandalized or otherwise used without your consent. Sad really.