As far as I'm concerned, yes, it would be okay for someone to start living there, and some jurisdictions at some times have had squatting laws that recognize this. Land is essentially a public resource; unlike manufactured goods, I can't create land, and if I claim ownership of a piece thereof, I can only do so by denying use of it to everyone else; the "it's mine and I'll do anything I want with it" property rights that correctly apply to manufactured goods, don't entirely apply to land. A case could be made for saying the same thing of public namespaces.
